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 $128.77   13.592%   $146.2724   $146.27   $146.25   $146.30  
  Purchase #2 $146.59   9.396%   $160.3636   $160.36   $160.35   $160.40  
  Purchase #3 $47.44   13.199%   $53.7016   $53.70   $53.70   $53.70  
  Purchase #4 $114.29   13.547%   $129.7729   $129.77   $129.75   $129.80  
  Purchase #5 $23.61   7.546%   $25.3916   $25.39   $25.40   $25.40  
  Purchase #6 $170.93   3.331%   $176.6237   $176.62   $176.60   $176.60  
  Purchase #7 $141.51   13.540%   $160.6705   $160.67   $160.65   $160.70  
  7 purchase totals = $773.14       $852.7963   $852.78   $852.70   $852.90