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 $190.93   12.623%   $215.0311   $215.03   $215.05   $215.00  
  Purchase #2 $144.71   7.111%   $155.0003   $155.00   $155.00   $155.00  
  Purchase #3 $229.92   6.539%   $244.9545   $244.95   $244.95   $245.00  
  Purchase #4 $153.33   4.768%   $160.6408   $160.64   $160.65   $160.60  
  Purchase #5 $125.74   5.759%   $132.9814   $132.98   $133.00   $133.00  
  Purchase #6 $16.37   8.388%   $17.7431   $17.74   $17.75   $17.70  
  Purchase #7 $128.92   12.814%   $145.4398   $145.44   $145.45   $145.40  
  7 purchase totals = $989.92       $1,071.7910   $1,071.78   $1,071.85   $1,071.70