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 $161.95   12.850%   $182.7606   $182.76   $182.75   $182.80  
  Purchase #2 $31.30   13.462%   $35.5136   $35.51   $35.50   $35.50  
  Purchase #3 $97.56   5.560%   $102.9843   $102.98   $103.00   $103.00  
  Purchase #4 $224.30   6.823%   $239.604   $239.60   $239.60   $239.60  
  Purchase #5 $119.47   12.602%   $134.5256   $134.53   $134.55   $134.50  
  Purchase #6 $178.70   12.657%   $201.3181   $201.32   $201.30   $201.30  
  Purchase #7 $141.52   7.291%   $151.8382   $151.84   $151.85   $151.80  
  7 purchase totals = $954.80       $1,048.5444   $1,048.54   $1,048.55   $1,048.50