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 $169.48   8.638%   $184.1197   $184.12   $184.10   $184.10  
  Purchase #2 $243.31   9.390%   $266.1568   $266.16   $266.15   $266.20  
  Purchase #3 $24.50   8.323%   $26.5391   $26.54   $26.55   $26.50  
  Purchase #4 $140.74   11.753%   $157.2812   $157.28   $157.30   $157.30  
  Purchase #5 $158.82   5.521%   $167.5885   $167.59   $167.60   $167.60  
  Purchase #6 $188.89   10.764%   $209.2221   $209.22   $209.20   $209.20  
  Purchase #7 $194.57   4.635%   $203.5883   $203.59   $203.60   $203.60  
  7 purchase totals = $1,120.31       $1,214.4957   $1,214.50   $1,214.50   $1,214.50