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 $47.67   4.235%   $49.6888   $49.69   $49.70   $49.70  
  Purchase #2 $118.60   3.367%   $122.5933   $122.59   $122.60   $122.60  
  Purchase #3 $23.82   5.322%   $25.0877   $25.09   $25.10   $25.10  
  Purchase #4 $93.33   6.642%   $99.529   $99.53   $99.55   $99.50  
  Purchase #5 $15.97   8.503%   $17.3279   $17.33   $17.35   $17.30  
  Purchase #6 $71.71   3.596%   $74.2887   $74.29   $74.30   $74.30  
  Purchase #7 $209.64   6.639%   $223.558   $223.56   $223.55   $223.60  
  7 purchase totals = $580.74       $612.0734   $612.08   $612.15   $612.10