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 $204.87   9.316%   $223.9557   $223.96   $223.95   $224.00  
  Purchase #2 $21.35   12.799%   $24.0826   $24.08   $24.10   $24.10  
  Purchase #3 $184.27   8.112%   $199.218   $199.22   $199.20   $199.20  
  Purchase #4 $13.71   3.513%   $14.1916   $14.19   $14.20   $14.20  
  Purchase #5 $191.79   8.194%   $207.5053   $207.51   $207.50   $207.50  
  Purchase #6 $205.97   4.492%   $215.2222   $215.22   $215.20   $215.20  
  Purchase #7 $200.39   9.520%   $219.4671   $219.47   $219.45   $219.50  
  7 purchase totals = $1,022.35       $1,103.6425   $1,103.65   $1,103.60   $1,103.70