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 $229.73   10.211%   $253.1877   $253.19   $253.20   $253.20  
  Purchase #2 $52.39   4.230%   $54.6061   $54.61   $54.60   $54.60  
  Purchase #3 $183.56   12.829%   $207.1089   $207.11   $207.10   $207.10  
  Purchase #4 $149.95   7.147%   $160.6669   $160.67   $160.65   $160.70  
  Purchase #5 $218.41   6.834%   $233.3361   $233.34   $233.35   $233.30  
  Purchase #6 $182.70   11.573%   $203.8439   $203.84   $203.85   $203.80  
  Purchase #7 $44.89   11.870%   $50.2184   $50.22   $50.20   $50.20  
  7 purchase totals = $1,061.63       $1,162.9680   $1,162.98   $1,162.95   $1,162.90