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 $187.78   11.874%   $210.077   $210.08   $210.10   $210.10  
  Purchase #2 $68.39   6.479%   $72.821   $72.82   $72.80   $72.80  
  Purchase #3 $87.77   10.682%   $97.1456   $97.15   $97.15   $97.10  
  Purchase #4 $216.59   4.787%   $226.9582   $226.96   $226.95   $227.00  
  Purchase #5 $236.80   9.739%   $259.862   $259.86   $259.85   $259.90  
  Purchase #6 $178.68   7.427%   $191.9506   $191.95   $191.95   $192.00  
  Purchase #7 $225.56   8.259%   $244.189   $244.19   $244.20   $244.20  
  7 purchase totals = $1,201.57       $1,303.0034   $1,303.01   $1,303.00   $1,303.10