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 $48.74   8.532%   $52.8985   $52.90   $52.90   $52.90  
  Purchase #2 $195.67   5.291%   $206.0229   $206.02   $206.00   $206.00  
  Purchase #3 $62.73   13.703%   $71.3259   $71.33   $71.35   $71.30  
  Purchase #4 $161.42   10.656%   $178.6209   $178.62   $178.60   $178.60  
  Purchase #5 $212.51   3.603%   $220.1667   $220.17   $220.15   $220.20  
  Purchase #6 $104.37   8.864%   $113.6214   $113.62   $113.60   $113.60  
  Purchase #7 $162.74   6.316%   $173.0187   $173.02   $173.00   $173.00  
  7 purchase totals = $948.18       $1,015.6750   $1,015.68   $1,015.60   $1,015.60