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 $54.62   5.613%   $57.6858   $57.69   $57.70   $57.70  
  Purchase #2 $124.65   12.835%   $140.6488   $140.65   $140.65   $140.60  
  Purchase #3 $53.80   8.333%   $58.2832   $58.28   $58.30   $58.30  
  Purchase #4 $227.75   3.766%   $236.3271   $236.33   $236.35   $236.30  
  Purchase #5 $59.26   9.146%   $64.6799   $64.68   $64.70   $64.70  
  Purchase #6 $234.87   10.587%   $259.7357   $259.74   $259.75   $259.70  
  Purchase #7 $194.72   9.368%   $212.9614   $212.96   $212.95   $213.00  
  7 purchase totals = $949.67       $1,030.3219   $1,030.33   $1,030.40   $1,030.30