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 $98.59   10.223%   $108.6689   $108.67   $108.65   $108.70  
  Purchase #2 $184.27   10.354%   $203.3493   $203.35   $203.35   $203.30  
  Purchase #3 $231.76   10.429%   $255.9303   $255.93   $255.95   $255.90  
  Purchase #4 $141.93   10.718%   $157.1421   $157.14   $157.15   $157.10  
  Purchase #5 $120.70   9.747%   $132.4646   $132.46   $132.45   $132.50  
  Purchase #6 $237.61   5.741%   $251.2512   $251.25   $251.25   $251.30  
  Purchase #7 $222.32   8.745%   $241.7619   $241.76   $241.75   $241.80  
  7 purchase totals = $1,237.18       $1,350.5683   $1,350.56   $1,350.55   $1,350.60