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 $31.26   7.417%   $33.5786   $33.58   $33.60   $33.60  
  Purchase #2 $196.81   5.383%   $207.4043   $207.40   $207.40   $207.40  
  Purchase #3 $80.42   11.772%   $89.887   $89.89   $89.90   $89.90  
  Purchase #4 $7.52   6.459%   $8.0057   $8.01   $8.00   $8.00  
  Purchase #5 $232.42   10.272%   $256.2942   $256.29   $256.30   $256.30  
  Purchase #6 $186.34   12.216%   $209.1033   $209.10   $209.10   $209.10  
  Purchase #7 $154.34   4.757%   $161.682   $161.68   $161.70   $161.70  
  7 purchase totals = $889.11       $965.9551   $965.95   $966.00   $966.00