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 $219.67   6.641%   $234.2583   $234.26   $234.25   $234.30  
  Purchase #2 $88.53   7.239%   $94.9387   $94.94   $94.95   $94.90  
  Purchase #3 $188.40   12.358%   $211.6825   $211.68   $211.70   $211.70  
  Purchase #4 $213.86   12.221%   $239.9958   $240.00   $240.00   $240.00  
  Purchase #5 $191.76   5.852%   $202.9818   $202.98   $203.00   $203.00  
  Purchase #6 $223.86   5.767%   $236.77   $236.77   $236.75   $236.80  
  Purchase #7 $136.25   13.797%   $155.0484   $155.05   $155.05   $155.00  
  7 purchase totals = $1,262.33       $1,375.6755   $1,375.68   $1,375.70   $1,375.70