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 $61.41   12.652%   $69.1796   $69.18   $69.20   $69.20  
  Purchase #2 $230.68   5.726%   $243.8887   $243.89   $243.90   $243.90  
  Purchase #3 $236.34   12.275%   $265.3507   $265.35   $265.35   $265.40  
  Purchase #4 $173.27   8.362%   $187.7588   $187.76   $187.75   $187.80  
  Purchase #5 $52.97   12.702%   $59.6982   $59.70   $59.70   $59.70  
  Purchase #6 $19.34   7.326%   $20.7568   $20.76   $20.75   $20.80  
  Purchase #7 $183.39   10.383%   $202.4314   $202.43   $202.45   $202.40  
  7 purchase totals = $957.40       $1,049.0642   $1,049.07   $1,049.10   $1,049.20