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 $66.85   9.851%   $73.4354   $73.44   $73.45   $73.40  
  Purchase #2 $120.89   7.694%   $130.1913   $130.19   $130.20   $130.20  
  Purchase #3 $129.61   5.235%   $136.3951   $136.40   $136.40   $136.40  
  Purchase #4 $9.80   9.616%   $10.7424   $10.74   $10.75   $10.70  
  Purchase #5 $194.56   13.451%   $220.7303   $220.73   $220.75   $220.70  
  Purchase #6 $226.99   6.553%   $241.8647   $241.86   $241.85   $241.90  
  Purchase #7 $197.90   7.123%   $211.9964   $212.00   $212.00   $212.00  
  7 purchase totals = $946.60       $1,025.3556   $1,025.36   $1,025.40   $1,025.30