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 $231.79   3.750%   $240.4821   $240.48   $240.50   $240.50  
  Purchase #2 $129.81   5.610%   $137.0923   $137.09   $137.10   $137.10  
  Purchase #3 $170.69   6.263%   $181.3803   $181.38   $181.40   $181.40  
  Purchase #4 $178.79   7.745%   $192.6373   $192.64   $192.65   $192.60  
  Purchase #5 $124.48   8.521%   $135.0869   $135.09   $135.10   $135.10  
  Purchase #6 $123.78   13.505%   $140.4965   $140.50   $140.50   $140.50  
  Purchase #7 $102.28   13.435%   $116.0213   $116.02   $116.00   $116.00  
  7 purchase totals = $1,061.62       $1,143.1967   $1,143.20   $1,143.25   $1,143.20