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 $250.76   10.399%   $276.8365   $276.84   $276.85   $276.80  
  Purchase #2 $51.76   5.848%   $54.7869   $54.79   $54.80   $54.80  
  Purchase #3 $69.96   4.171%   $72.878   $72.88   $72.90   $72.90  
  Purchase #4 $239.52   12.716%   $269.9774   $269.98   $270.00   $270.00  
  Purchase #5 $61.30   8.816%   $66.7042   $66.70   $66.70   $66.70  
  Purchase #6 $209.48   12.715%   $236.1154   $236.12   $236.10   $236.10  
  Purchase #7 $60.55   10.413%   $66.8551   $66.86   $66.85   $66.90  
  7 purchase totals = $943.33       $1,044.1535   $1,044.17   $1,044.20   $1,044.20