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 $51.66   13.808%   $58.7932   $58.79   $58.80   $58.80  
  Purchase #2 $233.36   5.455%   $246.0898   $246.09   $246.10   $246.10  
  Purchase #3 $211.28   10.657%   $233.7961   $233.80   $233.80   $233.80  
  Purchase #4 $65.77   11.568%   $73.3783   $73.38   $73.40   $73.40  
  Purchase #5 $130.38   11.807%   $145.774   $145.77   $145.75   $145.80  
  Purchase #6 $181.39   13.212%   $205.3552   $205.36   $205.35   $205.40  
  Purchase #7 $106.74   11.812%   $119.3481   $119.35   $119.35   $119.30  
  7 purchase totals = $980.58       $1,082.5347   $1,082.54   $1,082.55   $1,082.60