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 $246.92   11.712%   $275.8393   $275.84   $275.85   $275.80  
  Purchase #2 $175.41   12.856%   $197.9607   $197.96   $197.95   $198.00  
  Purchase #3 $190.49   11.483%   $212.364   $212.36   $212.35   $212.40  
  Purchase #4 $94.81   4.848%   $99.4064   $99.41   $99.40   $99.40  
  Purchase #5 $25.47   10.742%   $28.206   $28.21   $28.20   $28.20  
  Purchase #6 $131.50   8.270%   $142.3751   $142.38   $142.40   $142.40  
  Purchase #7 $51.43   12.800%   $58.013   $58.01   $58.00   $58.00  
  7 purchase totals = $916.03       $1,014.1645   $1,014.17   $1,014.15   $1,014.20