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 $86.35   8.480%   $93.6725   $93.67   $93.65   $93.70  
  Purchase #2 $22.34   13.768%   $25.4158   $25.42   $25.40   $25.40  
  Purchase #3 $48.57   12.141%   $54.4669   $54.47   $54.45   $54.50  
  Purchase #4 $170.74   3.290%   $176.3573   $176.36   $176.35   $176.40  
  Purchase #5 $153.40   9.144%   $167.4269   $167.43   $167.45   $167.40  
  Purchase #6 $72.38   7.302%   $77.6652   $77.67   $77.65   $77.70  
  Purchase #7 $116.43   10.650%   $128.8298   $128.83   $128.85   $128.80  
  7 purchase totals = $670.21       $723.8344   $723.85   $723.80   $723.90