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 $95.86   3.473%   $99.1892   $99.19   $99.20   $99.20  
  Purchase #2 $119.76   6.197%   $127.1815   $127.18   $127.20   $127.20  
  Purchase #3 $221.75   5.353%   $233.6203   $233.62   $233.60   $233.60  
  Purchase #4 $39.65   3.489%   $41.0334   $41.03   $41.05   $41.00  
  Purchase #5 $170.29   5.449%   $179.5691   $179.57   $179.55   $179.60  
  Purchase #6 $121.56   13.695%   $138.2076   $138.21   $138.20   $138.20  
  Purchase #7 $92.41   4.565%   $96.6285   $96.63   $96.65   $96.60  
  7 purchase totals = $861.28       $915.4296   $915.43   $915.45   $915.40