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 $60.98   6.343%   $64.848   $64.85   $64.85   $64.80  
  Purchase #2 $43.35   7.725%   $46.6988   $46.70   $46.70   $46.70  
  Purchase #3 $64.78   3.309%   $66.9236   $66.92   $66.90   $66.90  
  Purchase #4 $84.50   5.173%   $88.8712   $88.87   $88.85   $88.90  
  Purchase #5 $223.92   13.732%   $254.6687   $254.67   $254.65   $254.70  
  Purchase #6 $138.66   6.365%   $147.4857   $147.49   $147.50   $147.50  
  Purchase #7 $115.66   10.397%   $127.6852   $127.69   $127.70   $127.70  
  7 purchase totals = $731.85       $797.1812   $797.19   $797.15   $797.20