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 $184.67   10.164%   $203.4399   $203.44   $203.45   $203.40  
  Purchase #2 $225.79   10.527%   $249.5589   $249.56   $249.55   $249.60  
  Purchase #3 $246.67   5.421%   $260.042   $260.04   $260.05   $260.00  
  Purchase #4 $119.62   5.547%   $126.2553   $126.26   $126.25   $126.30  
  Purchase #5 $207.26   8.197%   $224.2491   $224.25   $224.25   $224.20  
  Purchase #6 $99.55   12.650%   $112.1431   $112.14   $112.15   $112.10  
  Purchase #7 $171.70   7.474%   $184.5329   $184.53   $184.55   $184.50  
  7 purchase totals = $1,255.26       $1,360.2212   $1,360.22   $1,360.25   $1,360.10