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 $71.29   6.350%   $75.8169   $75.82   $75.80   $75.80  
  Purchase #2 $217.51   6.711%   $232.1071   $232.11   $232.10   $232.10  
  Purchase #3 $5.70   7.177%   $6.1091   $6.11   $6.10   $6.10  
  Purchase #4 $184.29   12.731%   $207.752   $207.75   $207.75   $207.80  
  Purchase #5 $173.90   4.593%   $181.8872   $181.89   $181.90   $181.90  
  Purchase #6 $64.53   8.584%   $70.0693   $70.07   $70.05   $70.10  
  Purchase #7 $232.99   4.277%   $242.955   $242.96   $242.95   $243.00  
  7 purchase totals = $950.21       $1,016.6966   $1,016.71   $1,016.65   $1,016.80