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 $89.81   5.829%   $95.045   $95.05   $95.05   $95.00  
  Purchase #2 $74.90   13.354%   $84.9021   $84.90   $84.90   $84.90  
  Purchase #3 $103.35   6.682%   $110.2558   $110.26   $110.25   $110.30  
  Purchase #4 $182.94   13.549%   $207.7265   $207.73   $207.75   $207.70  
  Purchase #5 $145.98   8.282%   $158.0701   $158.07   $158.05   $158.10  
  Purchase #6 $170.71   12.782%   $192.5302   $192.53   $192.55   $192.50  
  Purchase #7 $202.41   8.490%   $219.5946   $219.59   $219.60   $219.60  
  7 purchase totals = $970.10       $1,068.1243   $1,068.13   $1,068.15   $1,068.10