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 $88.43   11.174%   $98.3112   $98.31   $98.30   $98.30  
  Purchase #2 $28.93   12.570%   $32.5665   $32.57   $32.55   $32.60  
  Purchase #3 $199.80   8.273%   $216.3295   $216.33   $216.35   $216.30  
  Purchase #4 $33.73   3.464%   $34.8984   $34.90   $34.90   $34.90  
  Purchase #5 $127.85   6.846%   $136.6026   $136.60   $136.60   $136.60  
  Purchase #6 $108.79   10.446%   $120.1542   $120.15   $120.15   $120.20  
  Purchase #7 $156.73   6.857%   $167.477   $167.48   $167.50   $167.50  
  7 purchase totals = $744.26       $806.3394   $806.34   $806.35   $806.40