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 $168.79   13.133%   $190.9572   $190.96   $190.95   $191.00  
  Purchase #2 $205.96   3.837%   $213.8627   $213.86   $213.85   $213.90  
  Purchase #3 $85.96   9.829%   $94.409   $94.41   $94.40   $94.40  
  Purchase #4 $217.98   9.322%   $238.3001   $238.30   $238.30   $238.30  
  Purchase #5 $204.47   13.755%   $232.5948   $232.59   $232.60   $232.60  
  Purchase #6 $24.50   11.495%   $27.3163   $27.32   $27.30   $27.30  
  Purchase #7 $123.86   7.152%   $132.7185   $132.72   $132.70   $132.70  
  7 purchase totals = $1,031.52       $1,130.1586   $1,130.16   $1,130.10   $1,130.20