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 $153.84   7.457%   $165.3118   $165.31   $165.30   $165.30  
  Purchase #2 $246.34   8.200%   $266.5399   $266.54   $266.55   $266.50  
  Purchase #3 $87.29   6.272%   $92.7648   $92.76   $92.75   $92.80  
  Purchase #4 $97.85   5.191%   $102.9294   $102.93   $102.95   $102.90  
  Purchase #5 $108.51   13.644%   $123.3151   $123.32   $123.30   $123.30  
  Purchase #6 $30.81   4.542%   $32.2094   $32.21   $32.20   $32.20  
  Purchase #7 $216.87   10.518%   $239.6804   $239.68   $239.70   $239.70  
  7 purchase totals = $941.51       $1,022.7508   $1,022.75   $1,022.75   $1,022.70