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 $242.61   10.536%   $268.1714   $268.17   $268.15   $268.20  
  Purchase #2 $183.51   7.481%   $197.2384   $197.24   $197.25   $197.20  
  Purchase #3 $213.53   7.148%   $228.7931   $228.79   $228.80   $228.80  
  Purchase #4 $220.91   9.794%   $242.5459   $242.55   $242.55   $242.50  
  Purchase #5 $48.98   6.565%   $52.1955   $52.20   $52.20   $52.20  
  Purchase #6 $99.79   7.581%   $107.3551   $107.36   $107.35   $107.40  
  Purchase #7 $209.72   11.719%   $234.2971   $234.30   $234.30   $234.30  
  7 purchase totals = $1,219.05       $1,330.5965   $1,330.61   $1,330.60   $1,330.60