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 $77.74   12.246%   $87.26   $87.26   $87.25   $87.30  
  Purchase #2 $214.56   13.159%   $242.794   $242.79   $242.80   $242.80  
  Purchase #3 $107.49   4.685%   $112.5259   $112.53   $112.55   $112.50  
  Purchase #4 $115.61   12.190%   $129.7029   $129.70   $129.70   $129.70  
  Purchase #5 $194.86   4.709%   $204.036   $204.04   $204.05   $204.00  
  Purchase #6 $70.76   7.204%   $75.8576   $75.86   $75.85   $75.90  
  Purchase #7 $172.95   12.619%   $194.7746   $194.77   $194.75   $194.80  
  7 purchase totals = $953.97       $1,046.9510   $1,046.95   $1,046.95   $1,047.00