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 $115.87   9.645%   $127.0457   $127.05   $127.05   $127.00  
  Purchase #2 $157.46   12.357%   $176.9173   $176.92   $176.90   $176.90  
  Purchase #3 $182.50   12.795%   $205.8509   $205.85   $205.85   $205.90  
  Purchase #4 $221.54   7.681%   $238.5565   $238.56   $238.55   $238.60  
  Purchase #5 $189.80   10.787%   $210.2737   $210.27   $210.25   $210.30  
  Purchase #6 $159.40   4.831%   $167.1006   $167.10   $167.10   $167.10  
  Purchase #7 $63.78   7.668%   $68.6707   $68.67   $68.65   $68.70  
  7 purchase totals = $1,090.35       $1,194.4154   $1,194.42   $1,194.35   $1,194.50