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 $66.91   11.759%   $74.7779   $74.78   $74.80   $74.80  
  Purchase #2 $56.48   3.753%   $58.5997   $58.60   $58.60   $58.60  
  Purchase #3 $97.67   9.843%   $107.2837   $107.28   $107.30   $107.30  
  Purchase #4 $240.53   8.228%   $260.3208   $260.32   $260.30   $260.30  
  Purchase #5 $182.26   13.539%   $206.9362   $206.94   $206.95   $206.90  
  Purchase #6 $162.40   13.201%   $183.8384   $183.84   $183.85   $183.80  
  Purchase #7 $142.38   3.670%   $147.6053   $147.61   $147.60   $147.60  
  7 purchase totals = $948.63       $1,039.3620   $1,039.37   $1,039.40   $1,039.30