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 $51.38   13.493%   $58.3127   $58.31   $58.30   $58.30  
  Purchase #2 $194.75   13.156%   $220.3713   $220.37   $220.35   $220.40  
  Purchase #3 $113.63   11.559%   $126.7645   $126.76   $126.75   $126.80  
  Purchase #4 $216.78   4.329%   $226.1644   $226.16   $226.15   $226.20  
  Purchase #5 $48.81   12.462%   $54.8927   $54.89   $54.90   $54.90  
  Purchase #6 $236.96   12.801%   $267.2932   $267.29   $267.30   $267.30  
  Purchase #7 $58.72   7.688%   $63.2344   $63.23   $63.25   $63.20  
  7 purchase totals = $921.03       $1,017.0332   $1,017.01   $1,017.00   $1,017.10