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 $168.96   8.344%   $183.058   $183.06   $183.05   $183.10  
  Purchase #2 $180.36   11.655%   $201.381   $201.38   $201.40   $201.40  
  Purchase #3 $101.54   11.849%   $113.5715   $113.57   $113.55   $113.60  
  Purchase #4 $164.28   10.282%   $181.1713   $181.17   $181.15   $181.20  
  Purchase #5 $193.39   11.852%   $216.3106   $216.31   $216.30   $216.30  
  Purchase #6 $28.64   5.102%   $30.1012   $30.10   $30.10   $30.10  
  Purchase #7 $150.42   5.340%   $158.4524   $158.45   $158.45   $158.50  
  7 purchase totals = $987.59       $1,084.0460   $1,084.04   $1,084.00   $1,084.20