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 $246.27   6.731%   $262.8464   $262.85   $262.85   $262.80  
  Purchase #2 $174.92   7.836%   $188.6267   $188.63   $188.65   $188.60  
  Purchase #3 $111.98   8.701%   $121.7234   $121.72   $121.70   $121.70  
  Purchase #4 $213.82   4.663%   $223.7904   $223.79   $223.80   $223.80  
  Purchase #5 $223.54   4.118%   $232.7454   $232.75   $232.75   $232.70  
  Purchase #6 $219.25   7.844%   $236.448   $236.45   $236.45   $236.40  
  Purchase #7 $137.93   11.386%   $153.6347   $153.63   $153.65   $153.60  
  7 purchase totals = $1,327.71       $1,419.8150   $1,419.82   $1,419.85   $1,419.60