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 $228.58   4.124%   $238.0066   $238.01   $238.00   $238.00  
  Purchase #2 $144.58   7.690%   $155.6982   $155.70   $155.70   $155.70  
  Purchase #3 $39.71   13.830%   $45.2019   $45.20   $45.20   $45.20  
  Purchase #4 $247.81   6.202%   $263.1792   $263.18   $263.20   $263.20  
  Purchase #5 $241.82   6.830%   $258.3363   $258.34   $258.35   $258.30  
  Purchase #6 $37.39   5.544%   $39.4629   $39.46   $39.45   $39.50  
  Purchase #7 $22.27   8.709%   $24.2095   $24.21   $24.20   $24.20  
  7 purchase totals = $962.16       $1,024.0946   $1,024.10   $1,024.10   $1,024.10