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 $90.33   6.804%   $96.4761   $96.48   $96.50   $96.50  
  Purchase #2 $201.34   7.533%   $216.5069   $216.51   $216.50   $216.50  
  Purchase #3 $200.78   11.735%   $224.3415   $224.34   $224.35   $224.30  
  Purchase #4 $59.99   13.768%   $68.2494   $68.25   $68.25   $68.20  
  Purchase #5 $170.33   11.225%   $189.4495   $189.45   $189.45   $189.40  
  Purchase #6 $63.53   3.207%   $65.5674   $65.57   $65.55   $65.60  
  Purchase #7 $211.69   9.133%   $231.0236   $231.02   $231.00   $231.00  
  7 purchase totals = $997.99       $1,091.6144   $1,091.62   $1,091.60   $1,091.50