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 $215.67   11.386%   $240.2262   $240.23   $240.25   $240.20  
  Purchase #2 $103.80   12.165%   $116.4273   $116.43   $116.45   $116.40  
  Purchase #3 $203.42   3.707%   $210.9608   $210.96   $210.95   $211.00  
  Purchase #4 $82.88   5.258%   $87.2378   $87.24   $87.25   $87.20  
  Purchase #5 $211.38   4.823%   $221.5749   $221.57   $221.55   $221.60  
  Purchase #6 $167.99   11.515%   $187.334   $187.33   $187.35   $187.30  
  Purchase #7 $88.27   7.871%   $95.2177   $95.22   $95.20   $95.20  
  7 purchase totals = $1,073.41       $1,158.9787   $1,158.98   $1,159.00   $1,158.90