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 $78.68   9.113%   $85.8501   $85.85   $85.85   $85.90  
  Purchase #2 $87.82   4.403%   $91.6867   $91.69   $91.70   $91.70  
  Purchase #3 $8.49   9.620%   $9.3067   $9.31   $9.30   $9.30  
  Purchase #4 $83.50   5.122%   $87.7769   $87.78   $87.80   $87.80  
  Purchase #5 $231.60   4.656%   $242.3833   $242.38   $242.40   $242.40  
  Purchase #6 $106.90   4.159%   $111.346   $111.35   $111.35   $111.30  
  Purchase #7 $151.95   5.824%   $160.7996   $160.80   $160.80   $160.80  
  7 purchase totals = $748.94       $789.1493   $789.16   $789.20   $789.20