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 $66.30   3.411%   $68.5615   $68.56   $68.55   $68.60  
  Purchase #2 $222.68   10.479%   $246.0146   $246.01   $246.00   $246.00  
  Purchase #3 $249.80   11.542%   $278.6319   $278.63   $278.65   $278.60  
  Purchase #4 $102.70   3.739%   $106.54   $106.54   $106.55   $106.50  
  Purchase #5 $211.98   11.751%   $236.8898   $236.89   $236.90   $236.90  
  Purchase #6 $203.86   7.153%   $218.4421   $218.44   $218.45   $218.40  
  Purchase #7 $156.33   11.406%   $174.161   $174.16   $174.15   $174.20  
  7 purchase totals = $1,213.65       $1,329.2409   $1,329.23   $1,329.25   $1,329.20