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 $85.30   11.123%   $94.7879   $94.79   $94.80   $94.80  
  Purchase #2 $64.45   3.485%   $66.6961   $66.70   $66.70   $66.70  
  Purchase #3 $232.65   6.820%   $248.5167   $248.52   $248.50   $248.50  
  Purchase #4 $15.78   13.631%   $17.931   $17.93   $17.95   $17.90  
  Purchase #5 $9.67   13.123%   $10.939   $10.94   $10.95   $10.90  
  Purchase #6 $109.29   3.823%   $113.4682   $113.47   $113.45   $113.50  
  Purchase #7 $191.90   10.383%   $211.825   $211.83   $211.85   $211.80  
  7 purchase totals = $709.04       $764.1639   $764.18   $764.20   $764.10