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 $227.48   8.238%   $246.2198   $246.22   $246.20   $246.20  
  Purchase #2 $151.75   12.427%   $170.608   $170.61   $170.60   $170.60  
  Purchase #3 $45.39   8.124%   $49.0775   $49.08   $49.10   $49.10  
  Purchase #4 $44.78   6.864%   $47.8537   $47.85   $47.85   $47.90  
  Purchase #5 $199.60   8.558%   $216.6818   $216.68   $216.70   $216.70  
  Purchase #6 $124.38   11.725%   $138.9636   $138.96   $138.95   $139.00  
  Purchase #7 $177.89   4.591%   $186.0569   $186.06   $186.05   $186.10  
  7 purchase totals = $971.27       $1,055.4613   $1,055.46   $1,055.45   $1,055.60