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 $88.67   9.293%   $96.9101   $96.91   $96.90   $96.90  
  Purchase #2 $87.29   10.808%   $96.7243   $96.72   $96.70   $96.70  
  Purchase #3 $157.74   9.829%   $173.2443   $173.24   $173.25   $173.20  
  Purchase #4 $204.67   12.836%   $230.9414   $230.94   $230.95   $230.90  
  Purchase #5 $117.30   13.740%   $133.417   $133.42   $133.40   $133.40  
  Purchase #6 $124.77   6.398%   $132.7528   $132.75   $132.75   $132.80  
  Purchase #7 $168.97   5.680%   $178.5675   $178.57   $178.55   $178.60  
  7 purchase totals = $949.41       $1,042.5574   $1,042.55   $1,042.50   $1,042.50