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 $88.32   3.346%   $91.2752   $91.28   $91.30   $91.30  
  Purchase #2 $118.56   10.521%   $131.0337   $131.03   $131.05   $131.00  
  Purchase #3 $60.92   12.430%   $68.4924   $68.49   $68.50   $68.50  
  Purchase #4 $113.44   11.539%   $126.5298   $126.53   $126.55   $126.50  
  Purchase #5 $227.48   12.363%   $255.6034   $255.60   $255.60   $255.60  
  Purchase #6 $47.67   8.366%   $51.6581   $51.66   $51.65   $51.70  
  Purchase #7 $27.82   12.711%   $31.3562   $31.36   $31.35   $31.40  
  7 purchase totals = $684.21       $755.9488   $755.95   $756.00   $756.00