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 $23.58   9.385%   $25.793   $25.79   $25.80   $25.80  
  Purchase #2 $60.81   7.498%   $65.3695   $65.37   $65.35   $65.40  
  Purchase #3 $220.41   9.180%   $240.6436   $240.64   $240.65   $240.60  
  Purchase #4 $75.87   12.331%   $85.2255   $85.23   $85.25   $85.20  
  Purchase #5 $167.38   7.791%   $180.4206   $180.42   $180.40   $180.40  
  Purchase #6 $244.72   12.546%   $275.4226   $275.42   $275.40   $275.40  
  Purchase #7 $178.58   6.111%   $189.493   $189.49   $189.50   $189.50  
  7 purchase totals = $971.35       $1,062.3678   $1,062.36   $1,062.35   $1,062.30