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 $92.92   6.302%   $98.7758   $98.78   $98.80   $98.80  
  Purchase #2 $96.57   10.690%   $106.8933   $106.89   $106.90   $106.90  
  Purchase #3 $206.78   5.836%   $218.8477   $218.85   $218.85   $218.80  
  Purchase #4 $88.72   11.212%   $98.6673   $98.67   $98.65   $98.70  
  Purchase #5 $236.64   12.272%   $265.6805   $265.68   $265.70   $265.70  
  Purchase #6 $205.43   7.597%   $221.0365   $221.04   $221.05   $221.00  
  Purchase #7 $6.73   3.127%   $6.9404   $6.94   $6.95   $6.90  
  7 purchase totals = $933.79       $1,016.8415   $1,016.85   $1,016.90   $1,016.80