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 $29.51   9.618%   $32.3483   $32.35   $32.35   $32.30  
  Purchase #2 $196.98   11.841%   $220.3044   $220.30   $220.30   $220.30  
  Purchase #3 $130.48   6.760%   $139.3004   $139.30   $139.30   $139.30  
  Purchase #4 $59.96   8.552%   $65.0878   $65.09   $65.10   $65.10  
  Purchase #5 $119.85   13.609%   $136.1604   $136.16   $136.15   $136.20  
  Purchase #6 $229.84   6.589%   $244.9842   $244.98   $245.00   $245.00  
  Purchase #7 $162.58   13.760%   $184.951   $184.95   $184.95   $185.00  
  7 purchase totals = $929.20       $1,023.1365   $1,023.13   $1,023.15   $1,023.20