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 $149.80   10.349%   $165.3028   $165.30   $165.30   $165.30  
  Purchase #2 $85.42   10.819%   $94.6616   $94.66   $94.65   $94.70  
  Purchase #3 $116.34   6.371%   $123.752   $123.75   $123.75   $123.80  
  Purchase #4 $57.58   5.192%   $60.5696   $60.57   $60.55   $60.60  
  Purchase #5 $176.31   7.286%   $189.1559   $189.16   $189.15   $189.20  
  Purchase #6 $230.92   4.409%   $241.1013   $241.10   $241.10   $241.10  
  Purchase #7 $78.51   11.810%   $87.782   $87.78   $87.80   $87.80  
  7 purchase totals = $894.88       $962.3252   $962.32   $962.30   $962.50