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 $22.63   13.722%   $25.7353   $25.74   $25.75   $25.70  
  Purchase #2 $132.55   13.442%   $150.3674   $150.37   $150.35   $150.40  
  Purchase #3 $181.27   10.190%   $199.7414   $199.74   $199.75   $199.70  
  Purchase #4 $158.78   13.159%   $179.6739   $179.67   $179.65   $179.70  
  Purchase #5 $229.58   6.637%   $244.8172   $244.82   $244.80   $244.80  
  Purchase #6 $223.52   13.439%   $253.5589   $253.56   $253.55   $253.60  
  Purchase #7 $199.51   9.558%   $218.5792   $218.58   $218.60   $218.60  
  7 purchase totals = $1,147.84       $1,272.4733   $1,272.48   $1,272.45   $1,272.50