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 $204.87   7.205%   $219.6309   $219.63   $219.65   $219.60  
  Purchase #2 $244.37   8.103%   $264.1713   $264.17   $264.15   $264.20  
  Purchase #3 $209.33   5.810%   $221.4921   $221.49   $221.50   $221.50  
  Purchase #4 $180.55   7.561%   $194.2014   $194.20   $194.20   $194.20  
  Purchase #5 $134.52   5.468%   $141.8756   $141.88   $141.90   $141.90  
  Purchase #6 $16.72   6.553%   $17.8157   $17.82   $17.80   $17.80  
  Purchase #7 $38.86   13.363%   $44.0529   $44.05   $44.05   $44.10  
  7 purchase totals = $1,029.22       $1,103.2399   $1,103.24   $1,103.25   $1,103.30