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 $206.36   11.297%   $229.6725   $229.67   $229.65   $229.70  
  Purchase #2 $240.92   10.783%   $266.8984   $266.90   $266.90   $266.90  
  Purchase #3 $121.95   10.270%   $134.4743   $134.47   $134.45   $134.50  
  Purchase #4 $203.75   6.199%   $216.3805   $216.38   $216.40   $216.40  
  Purchase #5 $103.93   4.726%   $108.8417   $108.84   $108.85   $108.80  
  Purchase #6 $217.42   7.755%   $234.2809   $234.28   $234.30   $234.30  
  Purchase #7 $30.98   10.331%   $34.1805   $34.18   $34.20   $34.20  
  7 purchase totals = $1,125.31       $1,224.7288   $1,224.72   $1,224.75   $1,224.80