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 $173.44   12.568%   $195.2379   $195.24   $195.25   $195.20  
  Purchase #2 $109.82   10.462%   $121.3094   $121.31   $121.30   $121.30  
  Purchase #3 $42.75   3.142%   $44.0932   $44.09   $44.10   $44.10  
  Purchase #4 $102.74   4.470%   $107.3325   $107.33   $107.35   $107.30  
  Purchase #5 $204.58   6.208%   $217.2803   $217.28   $217.30   $217.30  
  Purchase #6 $137.98   4.785%   $144.5823   $144.58   $144.60   $144.60  
  Purchase #7 $134.28   5.426%   $141.566   $141.57   $141.55   $141.60  
  7 purchase totals = $905.59       $971.4016   $971.40   $971.45   $971.40