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 $213.33   13.414%   $241.9461   $241.95   $241.95   $241.90  
  Purchase #2 $44.44   5.756%   $46.998   $47.00   $47.00   $47.00  
  Purchase #3 $99.77   9.543%   $109.2911   $109.29   $109.30   $109.30  
  Purchase #4 $220.48   6.860%   $235.6049   $235.60   $235.60   $235.60  
  Purchase #5 $228.55   11.755%   $255.4161   $255.42   $255.40   $255.40  
  Purchase #6 $21.72   11.402%   $24.1965   $24.20   $24.20   $24.20  
  Purchase #7 $48.80   12.559%   $54.9288   $54.93   $54.95   $54.90  
  7 purchase totals = $877.09       $968.3815   $968.39   $968.40   $968.30