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 $65.84   12.527%   $74.0878   $74.09   $74.10   $74.10  
  Purchase #2 $209.91   7.339%   $225.3153   $225.32   $225.30   $225.30  
  Purchase #3 $197.80   11.185%   $219.9239   $219.92   $219.90   $219.90  
  Purchase #4 $196.86   5.289%   $207.2719   $207.27   $207.25   $207.30  
  Purchase #5 $190.71   13.397%   $216.2594   $216.26   $216.25   $216.30  
  Purchase #6 $151.36   3.687%   $156.9406   $156.94   $156.95   $156.90  
  Purchase #7 $25.81   4.778%   $27.0432   $27.04   $27.05   $27.00  
  7 purchase totals = $1,038.29       $1,126.8421   $1,126.84   $1,126.80   $1,126.80