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 $229.62   13.543%   $260.7174   $260.72   $260.70   $260.70  
  Purchase #2 $57.72   9.139%   $62.995   $63.00   $63.00   $63.00  
  Purchase #3 $133.85   13.506%   $151.9278   $151.93   $151.95   $151.90  
  Purchase #4 $198.94   5.524%   $209.9294   $209.93   $209.95   $209.90  
  Purchase #5 $132.67   12.297%   $148.9844   $148.98   $149.00   $149.00  
  Purchase #6 $145.29   13.154%   $164.4014   $164.40   $164.40   $164.40  
  Purchase #7 $81.37   9.867%   $89.3988   $89.40   $89.40   $89.40  
  7 purchase totals = $979.46       $1,088.3542   $1,088.36   $1,088.40   $1,088.30