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 $241.67   7.782%   $260.4768   $260.48   $260.50   $260.50  
  Purchase #2 $140.28   3.131%   $144.6722   $144.67   $144.65   $144.70  
  Purchase #3 $99.98   12.265%   $112.2425   $112.24   $112.25   $112.20  
  Purchase #4 $199.27   12.128%   $223.4375   $223.44   $223.45   $223.40  
  Purchase #5 $161.52   12.417%   $181.5759   $181.58   $181.60   $181.60  
  Purchase #6 $76.82   4.159%   $80.0149   $80.01   $80.00   $80.00  
  Purchase #7 $248.44   6.230%   $263.9178   $263.92   $263.90   $263.90  
  7 purchase totals = $1,167.98       $1,266.3376   $1,266.34   $1,266.35   $1,266.30