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 $62.33   8.446%   $67.5944   $67.59   $67.60   $67.60  
  Purchase #2 $75.28   13.103%   $85.1439   $85.14   $85.15   $85.10  
  Purchase #3 $24.68   11.843%   $27.6029   $27.60   $27.60   $27.60  
  Purchase #4 $207.88   5.765%   $219.8643   $219.86   $219.85   $219.90  
  Purchase #5 $56.60   11.483%   $63.0994   $63.10   $63.10   $63.10  
  Purchase #6 $193.72   4.609%   $202.6486   $202.65   $202.65   $202.60  
  Purchase #7 $238.31   12.834%   $268.8947   $268.89   $268.90   $268.90  
  7 purchase totals = $858.80       $934.8482   $934.83   $934.85   $934.80