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 $218.80   9.470%   $239.5204   $239.52   $239.50   $239.50  
  Purchase #2 $31.42   5.735%   $33.2219   $33.22   $33.20   $33.20  
  Purchase #3 $185.77   9.279%   $203.0076   $203.01   $203.00   $203.00  
  Purchase #4 $56.31   10.675%   $62.3211   $62.32   $62.30   $62.30  
  Purchase #5 $217.84   13.695%   $247.6732   $247.67   $247.65   $247.70  
  Purchase #6 $180.71   10.332%   $199.381   $199.38   $199.40   $199.40  
  Purchase #7 $180.86   13.621%   $205.4949   $205.49   $205.50   $205.50  
  7 purchase totals = $1,071.71       $1,190.6201   $1,190.61   $1,190.55   $1,190.60