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 $171.93   11.380%   $191.4956   $191.50   $191.50   $191.50  
  Purchase #2 $68.98   6.824%   $73.6872   $73.69   $73.70   $73.70  
  Purchase #3 $207.77   5.424%   $219.0394   $219.04   $219.05   $219.00  
  Purchase #4 $162.97   12.661%   $183.6036   $183.60   $183.60   $183.60  
  Purchase #5 $206.42   6.582%   $220.0066   $220.01   $220.00   $220.00  
  Purchase #6 $69.83   5.759%   $73.8515   $73.85   $73.85   $73.90  
  Purchase #7 $57.40   8.518%   $62.2893   $62.29   $62.30   $62.30  
  7 purchase totals = $945.30       $1,023.9732   $1,023.98   $1,024.00   $1,024.00