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 $118.39   13.747%   $134.6651   $134.67   $134.65   $134.70  
  Purchase #2 $55.49   10.629%   $61.388   $61.39   $61.40   $61.40  
  Purchase #3 $184.42   9.715%   $202.3364   $202.34   $202.35   $202.30  
  Purchase #4 $210.83   5.284%   $221.9703   $221.97   $221.95   $222.00  
  Purchase #5 $58.73   4.633%   $61.451   $61.45   $61.45   $61.50  
  Purchase #6 $92.72   5.391%   $97.7185   $97.72   $97.70   $97.70  
  Purchase #7 $229.59   5.580%   $242.4011   $242.40   $242.40   $242.40  
  7 purchase totals = $950.17       $1,021.9304   $1,021.94   $1,021.90   $1,022.00