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 $56.61   5.221%   $59.5656   $59.57   $59.55   $59.60  
  Purchase #2 $119.94   4.750%   $125.6372   $125.64   $125.65   $125.60  
  Purchase #3 $5.54   9.238%   $6.0518   $6.05   $6.05   $6.10  
  Purchase #4 $243.64   11.515%   $271.6951   $271.70   $271.70   $271.70  
  Purchase #5 $61.48   9.180%   $67.1239   $67.12   $67.10   $67.10  
  Purchase #6 $180.92   10.156%   $199.2942   $199.29   $199.30   $199.30  
  Purchase #7 $135.31   7.507%   $145.4677   $145.47   $145.45   $145.50  
  7 purchase totals = $803.44       $874.8355   $874.84   $874.80   $874.90