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 $146.59   11.683%   $163.7161   $163.72   $163.70   $163.70  
  Purchase #2 $210.35   7.616%   $226.3703   $226.37   $226.35   $226.40  
  Purchase #3 $188.70   7.457%   $202.7714   $202.77   $202.75   $202.80  
  Purchase #4 $180.36   4.844%   $189.0966   $189.10   $189.10   $189.10  
  Purchase #5 $172.48   12.443%   $193.9417   $193.94   $193.95   $193.90  
  Purchase #6 $62.26   7.617%   $67.0023   $67.00   $67.00   $67.00  
  Purchase #7 $221.58   6.694%   $236.4126   $236.41   $236.40   $236.40  
  7 purchase totals = $1,182.32       $1,279.3110   $1,279.31   $1,279.25   $1,279.30