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 $183.28   4.145%   $190.877   $190.88   $190.90   $190.90  
  Purchase #2 $218.70   13.103%   $247.3563   $247.36   $247.35   $247.40  
  Purchase #3 $13.56   10.663%   $15.0059   $15.01   $15.00   $15.00  
  Purchase #4 $121.70   12.678%   $137.1291   $137.13   $137.15   $137.10  
  Purchase #5 $135.48   9.736%   $148.6703   $148.67   $148.65   $148.70  
  Purchase #6 $196.91   7.269%   $211.2234   $211.22   $211.20   $211.20  
  Purchase #7 $224.98   6.823%   $240.3304   $240.33   $240.35   $240.30  
  7 purchase totals = $1,094.61       $1,190.5924   $1,190.60   $1,190.60   $1,190.60