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 $134.65   8.445%   $146.0212   $146.02   $146.00   $146.00  
  Purchase #2 $152.51   6.224%   $162.0022   $162.00   $162.00   $162.00  
  Purchase #3 $157.89   10.147%   $173.9111   $173.91   $173.90   $173.90  
  Purchase #4 $93.78   6.837%   $100.1917   $100.19   $100.20   $100.20  
  Purchase #5 $181.94   10.711%   $201.4276   $201.43   $201.45   $201.40  
  Purchase #6 $117.94   6.128%   $125.1674   $125.17   $125.15   $125.20  
  Purchase #7 $122.91   7.663%   $132.3286   $132.33   $132.35   $132.30  
  7 purchase totals = $961.62       $1,041.0498   $1,041.05   $1,041.05   $1,041.00