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 $177.40   4.668%   $185.681   $185.68   $185.70   $185.70  
  Purchase #2 $24.32   8.119%   $26.2945   $26.29   $26.30   $26.30  
  Purchase #3 $50.98   5.671%   $53.8711   $53.87   $53.85   $53.90  
  Purchase #4 $193.56   6.180%   $205.522   $205.52   $205.50   $205.50  
  Purchase #5 $25.77   8.574%   $27.9795   $27.98   $28.00   $28.00  
  Purchase #6 $73.70   4.281%   $76.8551   $76.86   $76.85   $76.90  
  Purchase #7 $167.87   13.152%   $189.9483   $189.95   $189.95   $189.90  
  7 purchase totals = $713.60       $766.1515   $766.15   $766.15   $766.20