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 $170.93   12.797%   $192.8039   $192.80   $192.80   $192.80  
  Purchase #2 $183.69   5.584%   $193.9472   $193.95   $193.95   $193.90  
  Purchase #3 $181.65   11.199%   $201.993   $201.99   $202.00   $202.00  
  Purchase #4 $249.98   12.613%   $281.51   $281.51   $281.50   $281.50  
  Purchase #5 $111.33   6.440%   $118.4997   $118.50   $118.50   $118.50  
  Purchase #6 $156.63   3.507%   $162.123   $162.12   $162.10   $162.10  
  Purchase #7 $189.37   12.242%   $212.5527   $212.55   $212.55   $212.60  
  7 purchase totals = $1,243.58       $1,363.4295   $1,363.42   $1,363.40   $1,363.40