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 $162.82   11.762%   $181.9709   $181.97   $181.95   $182.00  
  Purchase #2 $221.79   13.585%   $251.9202   $251.92   $251.90   $251.90  
  Purchase #3 $67.69   3.342%   $69.9522   $69.95   $69.95   $70.00  
  Purchase #4 $92.28   6.117%   $97.9248   $97.92   $97.90   $97.90  
  Purchase #5 $65.25   10.242%   $71.9329   $71.93   $71.95   $71.90  
  Purchase #6 $213.78   4.625%   $223.6673   $223.67   $223.65   $223.70  
  Purchase #7 $184.94   4.432%   $193.1365   $193.14   $193.15   $193.10  
  7 purchase totals = $1,008.55       $1,090.5048   $1,090.50   $1,090.45   $1,090.50