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 $114.26   5.776%   $120.8597   $120.86   $120.85   $120.90  
  Purchase #2 $68.25   10.340%   $75.3071   $75.31   $75.30   $75.30  
  Purchase #3 $145.25   5.174%   $152.7652   $152.77   $152.75   $152.80  
  Purchase #4 $220.38   5.816%   $233.1973   $233.20   $233.20   $233.20  
  Purchase #5 $250.46   9.778%   $274.95   $274.95   $274.95   $275.00  
  Purchase #6 $74.74   5.396%   $78.773   $78.77   $78.75   $78.80  
  Purchase #7 $109.86   13.803%   $125.024   $125.02   $125.00   $125.00  
  7 purchase totals = $983.20       $1,060.8763   $1,060.88   $1,060.80   $1,061.00