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 $88.57   3.850%   $91.9799   $91.98   $92.00   $92.00  
  Purchase #2 $53.97   8.124%   $58.3545   $58.35   $58.35   $58.40  
  Purchase #3 $161.65   11.809%   $180.7392   $180.74   $180.75   $180.70  
  Purchase #4 $70.44   7.735%   $75.8885   $75.89   $75.90   $75.90  
  Purchase #5 $192.30   11.427%   $214.2741   $214.27   $214.25   $214.30  
  Purchase #6 $63.27   9.503%   $69.2825   $69.28   $69.30   $69.30  
  Purchase #7 $40.27   7.771%   $43.3994   $43.40   $43.40   $43.40  
  7 purchase totals = $670.47       $733.9181   $733.91   $733.95   $734.00