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 $82.25   12.169%   $92.259   $92.26   $92.25   $92.30  
  Purchase #2 $200.83   9.452%   $219.8125   $219.81   $219.80   $219.80  
  Purchase #3 $136.56   8.411%   $148.0461   $148.05   $148.05   $148.00  
  Purchase #4 $110.49   9.762%   $121.276   $121.28   $121.30   $121.30  
  Purchase #5 $194.97   8.203%   $210.9634   $210.96   $210.95   $211.00  
  Purchase #6 $123.80   3.135%   $127.6811   $127.68   $127.70   $127.70  
  Purchase #7 $236.44   10.495%   $261.2544   $261.25   $261.25   $261.30  
  7 purchase totals = $1,085.34       $1,181.2925   $1,181.29   $1,181.30   $1,181.40