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 $166.32   9.854%   $182.7092   $182.71   $182.70   $182.70  
  Purchase #2 $112.36   10.335%   $123.9724   $123.97   $123.95   $124.00  
  Purchase #3 $147.83   8.706%   $160.7001   $160.70   $160.70   $160.70  
  Purchase #4 $238.44   10.616%   $263.7528   $263.75   $263.75   $263.80  
  Purchase #5 $93.63   8.547%   $101.6326   $101.63   $101.65   $101.60  
  Purchase #6 $168.44   13.611%   $191.3664   $191.37   $191.35   $191.40  
  Purchase #7 $23.34   7.352%   $25.056   $25.06   $25.05   $25.10  
  7 purchase totals = $950.36       $1,049.1895   $1,049.19   $1,049.15   $1,049.30