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 $236.73   12.806%   $267.0456   $267.05   $267.05   $267.00  
  Purchase #2 $41.45   13.722%   $47.1378   $47.14   $47.15   $47.10  
  Purchase #3 $211.46   12.837%   $238.6051   $238.61   $238.60   $238.60  
  Purchase #4 $54.54   11.123%   $60.6065   $60.61   $60.60   $60.60  
  Purchase #5 $121.58   4.322%   $126.8347   $126.83   $126.85   $126.80  
  Purchase #6 $85.37   10.125%   $94.0137   $94.01   $94.00   $94.00  
  Purchase #7 $202.57   4.203%   $211.084   $211.08   $211.10   $211.10  
  7 purchase totals = $953.70       $1,045.3274   $1,045.33   $1,045.35   $1,045.20