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 $165.34   11.707%   $184.6964   $184.70   $184.70   $184.70  
  Purchase #2 $64.68   11.484%   $72.1079   $72.11   $72.10   $72.10  
  Purchase #3 $150.31   9.182%   $164.1115   $164.11   $164.10   $164.10  
  Purchase #4 $46.32   12.159%   $51.952   $51.95   $51.95   $52.00  
  Purchase #5 $94.76   10.392%   $104.6075   $104.61   $104.60   $104.60  
  Purchase #6 $56.40   10.576%   $62.3649   $62.36   $62.35   $62.40  
  Purchase #7 $204.52   4.553%   $213.8318   $213.83   $213.85   $213.80  
  7 purchase totals = $782.33       $853.6720   $853.67   $853.65   $853.70