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 $67.49   3.802%   $70.056   $70.06   $70.05   $70.10  
  Purchase #2 $147.96   11.581%   $165.0952   $165.10   $165.10   $165.10  
  Purchase #3 $170.83   6.431%   $181.8161   $181.82   $181.80   $181.80  
  Purchase #4 $140.76   4.774%   $147.4799   $147.48   $147.50   $147.50  
  Purchase #5 $179.94   10.528%   $198.8841   $198.88   $198.90   $198.90  
  Purchase #6 $193.97   11.129%   $215.5569   $215.56   $215.55   $215.60  
  Purchase #7 $211.31   13.381%   $239.5854   $239.59   $239.60   $239.60  
  7 purchase totals = $1,112.26       $1,218.4736   $1,218.49   $1,218.50   $1,218.60