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 $57.58   10.280%   $63.4992   $63.50   $63.50   $63.50  
  Purchase #2 $172.91   9.225%   $188.8609   $188.86   $188.85   $188.90  
  Purchase #3 $113.64   9.363%   $124.2801   $124.28   $124.30   $124.30  
  Purchase #4 $151.94   6.594%   $161.9589   $161.96   $161.95   $162.00  
  Purchase #5 $83.56   9.198%   $91.2458   $91.25   $91.25   $91.20  
  Purchase #6 $222.31   6.600%   $236.9825   $236.98   $237.00   $237.00  
  Purchase #7 $121.41   8.479%   $131.7044   $131.70   $131.70   $131.70  
  7 purchase totals = $923.35       $998.5318   $998.53   $998.55   $998.60