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 $92.32   10.165%   $101.7043   $101.70   $101.70   $101.70  
  Purchase #2 $224.58   13.704%   $255.3564   $255.36   $255.35   $255.40  
  Purchase #3 $28.96   3.306%   $29.9174   $29.92   $29.90   $29.90  
  Purchase #4 $23.51   7.251%   $25.2147   $25.21   $25.20   $25.20  
  Purchase #5 $134.56   12.448%   $151.31   $151.31   $151.30   $151.30  
  Purchase #6 $243.75   12.761%   $274.8549   $274.85   $274.85   $274.90  
  Purchase #7 $212.93   12.344%   $239.2141   $239.21   $239.20   $239.20  
  7 purchase totals = $960.61       $1,077.5718   $1,077.56   $1,077.50   $1,077.60