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 $219.87   13.731%   $250.0603   $250.06   $250.05   $250.10  
  Purchase #2 $203.54   10.361%   $224.6288   $224.63   $224.65   $224.60  
  Purchase #3 $151.74   12.102%   $170.1036   $170.10   $170.10   $170.10  
  Purchase #4 $85.73   6.137%   $90.9913   $90.99   $91.00   $91.00  
  Purchase #5 $67.49   5.463%   $71.177   $71.18   $71.20   $71.20  
  Purchase #6 $188.56   7.625%   $202.9377   $202.94   $202.95   $202.90  
  Purchase #7 $44.45   9.641%   $48.7354   $48.74   $48.75   $48.70  
  7 purchase totals = $961.38       $1,058.6341   $1,058.64   $1,058.70   $1,058.60