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 $122.96   4.322%   $128.2743   $128.27   $128.25   $128.30  
  Purchase #2 $160.47   4.502%   $167.6944   $167.69   $167.70   $167.70  
  Purchase #3 $130.52   12.122%   $146.3416   $146.34   $146.35   $146.30  
  Purchase #4 $8.79   3.623%   $9.1085   $9.11   $9.10   $9.10  
  Purchase #5 $7.31   10.702%   $8.0923   $8.09   $8.10   $8.10  
  Purchase #6 $129.52   9.434%   $141.7389   $141.74   $141.75   $141.70  
  Purchase #7 $93.66   5.235%   $98.5631   $98.56   $98.55   $98.60  
  7 purchase totals = $653.23       $699.8131   $699.80   $699.80   $699.80