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 $195.63   7.511%   $210.3238   $210.32   $210.30   $210.30  
  Purchase #2 $78.82   10.458%   $87.063   $87.06   $87.05   $87.10  
  Purchase #3 $116.60   12.121%   $130.7331   $130.73   $130.75   $130.70  
  Purchase #4 $24.44   9.576%   $26.7804   $26.78   $26.80   $26.80  
  Purchase #5 $243.30   11.700%   $271.7661   $271.77   $271.75   $271.80  
  Purchase #6 $46.78   6.462%   $49.8029   $49.80   $49.80   $49.80  
  Purchase #7 $242.25   5.392%   $255.3121   $255.31   $255.30   $255.30  
  7 purchase totals = $947.82       $1,031.7814   $1,031.77   $1,031.75   $1,031.80