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 $165.62   5.869%   $175.3402   $175.34   $175.35   $175.30  
  Purchase #2 $59.84   11.148%   $66.511   $66.51   $66.50   $66.50  
  Purchase #3 $53.83   3.182%   $55.5429   $55.54   $55.55   $55.50  
  Purchase #4 $124.62   11.321%   $138.7282   $138.73   $138.75   $138.70  
  Purchase #5 $230.44   10.450%   $254.521   $254.52   $254.50   $254.50  
  Purchase #6 $65.43   3.569%   $67.7652   $67.77   $67.75   $67.80  
  Purchase #7 $185.53   9.557%   $203.2611   $203.26   $203.25   $203.30  
  7 purchase totals = $885.31       $961.6696   $961.67   $961.65   $961.60