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 $46.35   11.712%   $51.7785   $51.78   $51.80   $51.80  
  Purchase #2 $14.95   5.137%   $15.718   $15.72   $15.70   $15.70  
  Purchase #3 $66.64   5.262%   $70.1466   $70.15   $70.15   $70.10  
  Purchase #4 $205.35   3.441%   $212.4161   $212.42   $212.40   $212.40  
  Purchase #5 $206.89   7.272%   $221.935   $221.94   $221.95   $221.90  
  Purchase #6 $209.74   9.148%   $228.927   $228.93   $228.95   $228.90  
  Purchase #7 $231.98   13.338%   $262.9215   $262.92   $262.90   $262.90  
  7 purchase totals = $981.90       $1,063.8427   $1,063.86   $1,063.85   $1,063.70