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 $126.27   8.373%   $136.8426   $136.84   $136.85   $136.80  
  Purchase #2 $32.96   5.453%   $34.7573   $34.76   $34.75   $34.80  
  Purchase #3 $200.99   11.252%   $223.6054   $223.61   $223.60   $223.60  
  Purchase #4 $101.74   9.598%   $111.505   $111.51   $111.50   $111.50  
  Purchase #5 $181.56   6.681%   $193.69   $193.69   $193.70   $193.70  
  Purchase #6 $51.54   12.682%   $58.0763   $58.08   $58.10   $58.10  
  Purchase #7 $244.82   8.502%   $265.6346   $265.63   $265.65   $265.60  
  7 purchase totals = $939.88       $1,024.1112   $1,024.12   $1,024.15   $1,024.10