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 $228.32   10.753%   $252.8712   $252.87   $252.85   $252.90  
  Purchase #2 $195.77   3.103%   $201.8447   $201.84   $201.85   $201.80  
  Purchase #3 $220.72   11.531%   $246.1712   $246.17   $246.15   $246.20  
  Purchase #4 $5.33   9.160%   $5.8182   $5.82   $5.80   $5.80  
  Purchase #5 $69.94   12.688%   $78.814   $78.81   $78.80   $78.80  
  Purchase #6 $22.29   3.805%   $23.1381   $23.14   $23.15   $23.10  
  Purchase #7 $217.29   4.853%   $227.8351   $227.84   $227.85   $227.80  
  7 purchase totals = $959.66       $1,036.4925   $1,036.49   $1,036.45   $1,036.40