Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $177.63   11.760%   $198.5193   $198.52   $198.50   $198.50  
  Purchase #2 $245.54   3.447%   $254.0038   $254.00   $254.00   $254.00  
  Purchase #3 $202.48   7.692%   $218.0548   $218.05   $218.05   $218.10  
  Purchase #4 $103.47   6.649%   $110.3497   $110.35   $110.35   $110.30  
  Purchase #5 $119.80   12.642%   $134.9451   $134.95   $134.95   $134.90  
  Purchase #6 $170.60   7.274%   $183.0094   $183.01   $183.00   $183.00  
  Purchase #7 $139.55   8.717%   $151.7146   $151.71   $151.70   $151.70  
  7 purchase totals = $1,159.07       $1,250.5967   $1,250.59   $1,250.55   $1,250.50