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 $249.85   5.290%   $263.0671   $263.07   $263.05   $263.10  
  Purchase #2 $53.84   8.791%   $58.5731   $58.57   $58.55   $58.60  
  Purchase #3 $250.31   5.584%   $264.2873   $264.29   $264.30   $264.30  
  Purchase #4 $6.36   6.288%   $6.7599   $6.76   $6.75   $6.80  
  Purchase #5 $141.57   10.195%   $156.0031   $156.00   $156.00   $156.00  
  Purchase #6 $192.66   9.403%   $210.7758   $210.78   $210.80   $210.80  
  Purchase #7 $159.93   4.451%   $167.0485   $167.05   $167.05   $167.00  
  7 purchase totals = $1,054.52       $1,126.5148   $1,126.52   $1,126.50   $1,126.60