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 $88.65   4.535%   $92.6703   $92.67   $92.65   $92.70  
  Purchase #2 $96.83   5.689%   $102.3387   $102.34   $102.35   $102.30  
  Purchase #3 $53.99   5.178%   $56.7856   $56.79   $56.80   $56.80  
  Purchase #4 $174.84   5.338%   $184.173   $184.17   $184.15   $184.20  
  Purchase #5 $246.77   6.855%   $263.6861   $263.69   $263.70   $263.70  
  Purchase #6 $22.85   7.372%   $24.5345   $24.53   $24.55   $24.50  
  Purchase #7 $104.98   13.471%   $119.1219   $119.12   $119.10   $119.10  
  7 purchase totals = $788.91       $843.3101   $843.31   $843.30   $843.30