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 $96.86   12.779%   $109.2377   $109.24   $109.25   $109.20  
  Purchase #2 $152.73   11.552%   $170.3734   $170.37   $170.35   $170.40  
  Purchase #3 $34.27   6.610%   $36.5352   $36.54   $36.55   $36.50  
  Purchase #4 $62.48   3.521%   $64.6799   $64.68   $64.70   $64.70  
  Purchase #5 $148.53   9.320%   $162.373   $162.37   $162.35   $162.40  
  Purchase #6 $224.60   8.208%   $243.0352   $243.04   $243.05   $243.00  
  Purchase #7 $17.37   5.357%   $18.3005   $18.30   $18.30   $18.30  
  7 purchase totals = $736.84       $804.5349   $804.54   $804.55   $804.50