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 $220.26   12.292%   $247.3344   $247.33   $247.35   $247.30  
  Purchase #2 $38.52   11.285%   $42.867   $42.87   $42.85   $42.90  
  Purchase #3 $160.79   5.480%   $169.6013   $169.60   $169.60   $169.60  
  Purchase #4 $23.27   4.438%   $24.3027   $24.30   $24.30   $24.30  
  Purchase #5 $222.27   4.158%   $231.512   $231.51   $231.50   $231.50  
  Purchase #6 $153.29   3.349%   $158.4237   $158.42   $158.40   $158.40  
  Purchase #7 $17.39   12.321%   $19.5326   $19.53   $19.55   $19.50  
  7 purchase totals = $835.79       $893.5737   $893.56   $893.55   $893.50