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 $61.34   4.725%   $64.2383   $64.24   $64.25   $64.20  
  Purchase #2 $79.68   4.242%   $83.06   $83.06   $83.05   $83.10  
  Purchase #3 $102.52   4.612%   $107.2482   $107.25   $107.25   $107.20  
  Purchase #4 $43.94   7.801%   $47.3678   $47.37   $47.35   $47.40  
  Purchase #5 $187.80   7.631%   $202.131   $202.13   $202.15   $202.10  
  Purchase #6 $175.89   5.450%   $185.476   $185.48   $185.50   $185.50  
  Purchase #7 $245.94   5.244%   $258.8371   $258.84   $258.85   $258.80  
  7 purchase totals = $897.11       $948.3584   $948.37   $948.40   $948.30