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 $245.93   8.402%   $266.593   $266.59   $266.60   $266.60  
  Purchase #2 $106.53   10.819%   $118.0555   $118.06   $118.05   $118.10  
  Purchase #3 $231.98   4.658%   $242.7856   $242.79   $242.80   $242.80  
  Purchase #4 $188.71   5.836%   $199.7231   $199.72   $199.70   $199.70  
  Purchase #5 $155.82   7.140%   $166.9455   $166.95   $166.95   $166.90  
  Purchase #6 $189.69   3.860%   $197.012   $197.01   $197.00   $197.00  
  Purchase #7 $5.25   11.292%   $5.8428   $5.84   $5.85   $5.80  
  7 purchase totals = $1,123.91       $1,196.9575   $1,196.96   $1,196.95   $1,196.90