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 $36.79   8.263%   $39.83   $39.83   $39.85   $39.80  
  Purchase #2 $134.35   11.432%   $149.7089   $149.71   $149.70   $149.70  
  Purchase #3 $47.33   13.506%   $53.7224   $53.72   $53.70   $53.70  
  Purchase #4 $217.85   12.173%   $244.3689   $244.37   $244.35   $244.40  
  Purchase #5 $5.79   5.661%   $6.1178   $6.12   $6.10   $6.10  
  Purchase #6 $215.35   12.690%   $242.6779   $242.68   $242.70   $242.70  
  Purchase #7 $250.49   9.803%   $275.0455   $275.05   $275.05   $275.00  
  7 purchase totals = $907.95       $1,011.4714   $1,011.48   $1,011.45   $1,011.40