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 $34.66   8.265%   $37.5246   $37.52   $37.50   $37.50  
  Purchase #2 $19.84   13.804%   $22.5787   $22.58   $22.60   $22.60  
  Purchase #3 $12.63   11.512%   $14.084   $14.08   $14.10   $14.10  
  Purchase #4 $245.97   4.118%   $256.099   $256.10   $256.10   $256.10  
  Purchase #5 $210.25   9.221%   $229.6372   $229.64   $229.65   $229.60  
  Purchase #6 $23.89   9.524%   $26.1653   $26.17   $26.15   $26.20  
  Purchase #7 $60.60   9.620%   $66.4297   $66.43   $66.45   $66.40  
  7 purchase totals = $607.84       $652.5185   $652.52   $652.55   $652.50