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 $181.26   11.457%   $202.027   $202.03   $202.05   $202.00  
  Purchase #2 $249.74   7.564%   $268.6303   $268.63   $268.65   $268.60  
  Purchase #3 $88.38   11.553%   $98.5905   $98.59   $98.60   $98.60  
  Purchase #4 $41.62   6.223%   $44.21   $44.21   $44.20   $44.20  
  Purchase #5 $89.85   7.740%   $96.8044   $96.80   $96.80   $96.80  
  Purchase #6 $53.58   13.504%   $60.8154   $60.82   $60.80   $60.80  
  Purchase #7 $91.42   8.835%   $99.497   $99.50   $99.50   $99.50  
  7 purchase totals = $795.85       $870.5746   $870.58   $870.60   $870.50