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 $53.88   8.351%   $58.3795   $58.38   $58.40   $58.40  
  Purchase #2 $6.90   3.669%   $7.1532   $7.15   $7.15   $7.20  
  Purchase #3 $141.27   7.152%   $151.3736   $151.37   $151.35   $151.40  
  Purchase #4 $140.82   10.415%   $155.4864   $155.49   $155.50   $155.50  
  Purchase #5 $196.33   7.293%   $210.6483   $210.65   $210.65   $210.60  
  Purchase #6 $247.97   5.833%   $262.4341   $262.43   $262.45   $262.40  
  Purchase #7 $202.79   13.828%   $230.8318   $230.83   $230.85   $230.80  
  7 purchase totals = $989.96       $1,076.3069   $1,076.30   $1,076.35   $1,076.30