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 $93.69   7.492%   $100.7093   $100.71   $100.70   $100.70  
  Purchase #2 $221.95   5.486%   $234.1262   $234.13   $234.15   $234.10  
  Purchase #3 $75.71   8.384%   $82.0575   $82.06   $82.05   $82.10  
  Purchase #4 $58.60   6.596%   $62.4653   $62.47   $62.45   $62.50  
  Purchase #5 $124.33   6.582%   $132.5134   $132.51   $132.50   $132.50  
  Purchase #6 $192.44   10.671%   $212.9753   $212.98   $213.00   $213.00  
  Purchase #7 $176.56   3.139%   $182.1022   $182.10   $182.10   $182.10  
  7 purchase totals = $943.28       $1,006.9492   $1,006.96   $1,006.95   $1,007.00