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 $24.41   6.227%   $25.93   $25.93   $25.95   $25.90  
  Purchase #2 $56.28   3.254%   $58.1114   $58.11   $58.10   $58.10  
  Purchase #3 $151.63   3.682%   $157.213   $157.21   $157.20   $157.20  
  Purchase #4 $34.78   10.598%   $38.466   $38.47   $38.45   $38.50  
  Purchase #5 $86.68   8.672%   $94.1969   $94.20   $94.20   $94.20  
  Purchase #6 $138.35   5.753%   $146.3093   $146.31   $146.30   $146.30  
  Purchase #7 $74.45   8.647%   $80.8877   $80.89   $80.90   $80.90  
  7 purchase totals = $566.58       $601.1143   $601.12   $601.10   $601.10