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 $250.54   4.849%   $262.6887   $262.69   $262.70   $262.70  
  Purchase #2 $108.28   10.571%   $119.7263   $119.73   $119.75   $119.70  
  Purchase #3 $40.62   6.599%   $43.3005   $43.30   $43.30   $43.30  
  Purchase #4 $163.80   4.104%   $170.5224   $170.52   $170.50   $170.50  
  Purchase #5 $60.84   9.628%   $66.6977   $66.70   $66.70   $66.70  
  Purchase #6 $187.66   7.790%   $202.2787   $202.28   $202.30   $202.30  
  Purchase #7 $133.70   7.200%   $143.3264   $143.33   $143.35   $143.30  
  7 purchase totals = $945.44       $1,008.5407   $1,008.55   $1,008.60   $1,008.50