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 $69.46   6.557%   $74.0145   $74.01   $74.00   $74.00  
  Purchase #2 $96.74   13.663%   $109.9576   $109.96   $109.95   $110.00  
  Purchase #3 $26.39   7.690%   $28.4194   $28.42   $28.40   $28.40  
  Purchase #4 $132.68   6.582%   $141.413   $141.41   $141.40   $141.40  
  Purchase #5 $182.76   9.751%   $200.5809   $200.58   $200.60   $200.60  
  Purchase #6 $219.49   11.141%   $243.9434   $243.94   $243.95   $243.90  
  Purchase #7 $44.64   13.799%   $50.7999   $50.80   $50.80   $50.80  
  7 purchase totals = $772.16       $849.1287   $849.12   $849.10   $849.10