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 $84.61   11.275%   $94.1498   $94.15   $94.15   $94.10  
  Purchase #2 $73.28   12.169%   $82.1974   $82.20   $82.20   $82.20  
  Purchase #3 $155.64   9.511%   $170.4429   $170.44   $170.45   $170.40  
  Purchase #4 $5.35   13.375%   $6.0656   $6.07   $6.05   $6.10  
  Purchase #5 $67.39   7.829%   $72.666   $72.67   $72.65   $72.70  
  Purchase #6 $125.69   6.776%   $134.2068   $134.21   $134.20   $134.20  
  Purchase #7 $36.85   13.439%   $41.8023   $41.80   $41.80   $41.80  
  7 purchase totals = $548.81       $601.5308   $601.54   $601.50   $601.50