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 $197.89   5.758%   $209.2845   $209.28   $209.30   $209.30  
  Purchase #2 $92.71   9.209%   $101.2477   $101.25   $101.25   $101.20  
  Purchase #3 $60.28   12.327%   $67.7107   $67.71   $67.70   $67.70  
  Purchase #4 $189.95   7.315%   $203.8448   $203.84   $203.85   $203.80  
  Purchase #5 $165.65   12.167%   $185.8046   $185.80   $185.80   $185.80  
  Purchase #6 $98.29   5.411%   $103.6085   $103.61   $103.60   $103.60  
  Purchase #7 $189.81   11.188%   $211.0459   $211.05   $211.05   $211.00  
  7 purchase totals = $994.58       $1,082.5467   $1,082.54   $1,082.55   $1,082.40