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 $44.90   9.142%   $49.0048   $49.00   $49.00   $49.00  
  Purchase #2 $209.28   10.386%   $231.0158   $231.02   $231.00   $231.00  
  Purchase #3 $59.48   3.688%   $61.6736   $61.67   $61.65   $61.70  
  Purchase #4 $68.73   5.535%   $72.5342   $72.53   $72.55   $72.50  
  Purchase #5 $204.58   4.221%   $213.2153   $213.22   $213.20   $213.20  
  Purchase #6 $190.40   4.230%   $198.4539   $198.45   $198.45   $198.50  
  Purchase #7 $179.70   5.573%   $189.7147   $189.71   $189.70   $189.70  
  7 purchase totals = $957.07       $1,015.6123   $1,015.60   $1,015.55   $1,015.60