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 $184.84   9.828%   $203.0061   $203.01   $203.00   $203.00  
  Purchase #2 $248.94   6.394%   $264.8572   $264.86   $264.85   $264.90  
  Purchase #3 $250.30   6.645%   $266.9324   $266.93   $266.95   $266.90  
  Purchase #4 $195.87   12.483%   $220.3205   $220.32   $220.30   $220.30  
  Purchase #5 $234.80   12.850%   $264.9718   $264.97   $264.95   $265.00  
  Purchase #6 $22.79   6.246%   $24.2135   $24.21   $24.20   $24.20  
  Purchase #7 $39.48   10.516%   $43.6317   $43.63   $43.65   $43.60  
  7 purchase totals = $1,177.02       $1,287.9332   $1,287.93   $1,287.90   $1,287.90