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 $221.87   8.533%   $240.8022   $240.80   $240.80   $240.80  
  Purchase #2 $210.34   10.462%   $232.3458   $232.35   $232.35   $232.30  
  Purchase #3 $178.38   8.345%   $193.2658   $193.27   $193.25   $193.30  
  Purchase #4 $39.62   11.206%   $44.0598   $44.06   $44.05   $44.10  
  Purchase #5 $95.94   12.758%   $108.18   $108.18   $108.20   $108.20  
  Purchase #6 $211.74   11.601%   $236.304   $236.30   $236.30   $236.30  
  Purchase #7 $134.74   11.416%   $150.1219   $150.12   $150.10   $150.10  
  7 purchase totals = $1,092.63       $1,205.0795   $1,205.08   $1,205.05   $1,205.10