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 $212.78   13.252%   $240.9776   $240.98   $241.00   $241.00  
  Purchase #2 $183.82   12.276%   $206.3857   $206.39   $206.40   $206.40  
  Purchase #3 $63.96   12.750%   $72.1149   $72.11   $72.10   $72.10  
  Purchase #4 $14.66   12.506%   $16.4934   $16.49   $16.50   $16.50  
  Purchase #5 $181.75   12.226%   $203.9708   $203.97   $203.95   $204.00  
  Purchase #6 $38.55   6.370%   $41.0056   $41.01   $41.00   $41.00  
  Purchase #7 $232.38   10.412%   $256.5754   $256.58   $256.60   $256.60  
  7 purchase totals = $927.90       $1,037.5234   $1,037.53   $1,037.55   $1,037.60