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 $226.96   11.481%   $253.0173   $253.02   $253.00   $253.00  
  Purchase #2 $113.79   9.186%   $124.2427   $124.24   $124.25   $124.20  
  Purchase #3 $161.55   12.453%   $181.6678   $181.67   $181.65   $181.70  
  Purchase #4 $128.30   7.237%   $137.5851   $137.59   $137.60   $137.60  
  Purchase #5 $191.77   5.513%   $202.3423   $202.34   $202.35   $202.30  
  Purchase #6 $21.51   8.635%   $23.3674   $23.37   $23.35   $23.40  
  Purchase #7 $244.68   13.743%   $278.3064   $278.31   $278.30   $278.30  
  7 purchase totals = $1,088.56       $1,200.5290   $1,200.54   $1,200.50   $1,200.50