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 $84.87   11.441%   $94.58   $94.58   $94.60   $94.60  
  Purchase #2 $91.75   4.102%   $95.5136   $95.51   $95.50   $95.50  
  Purchase #3 $238.47   5.612%   $251.8529   $251.85   $251.85   $251.90  
  Purchase #4 $232.53   10.810%   $257.6665   $257.67   $257.65   $257.70  
  Purchase #5 $154.85   4.295%   $161.5008   $161.50   $161.50   $161.50  
  Purchase #6 $25.32   7.713%   $27.2729   $27.27   $27.25   $27.30  
  Purchase #7 $243.27   13.579%   $276.3036   $276.30   $276.30   $276.30  
  7 purchase totals = $1,071.06       $1,164.6903   $1,164.68   $1,164.65   $1,164.80