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 $96.36   8.172%   $104.2345   $104.23   $104.25   $104.20  
  Purchase #2 $134.52   11.283%   $149.6979   $149.70   $149.70   $149.70  
  Purchase #3 $56.45   8.170%   $61.062   $61.06   $61.05   $61.10  
  Purchase #4 $77.52   12.278%   $87.0379   $87.04   $87.05   $87.00  
  Purchase #5 $166.59   6.207%   $176.9302   $176.93   $176.95   $176.90  
  Purchase #6 $26.98   10.834%   $29.903   $29.90   $29.90   $29.90  
  Purchase #7 $211.67   5.739%   $223.8177   $223.82   $223.80   $223.80  
  7 purchase totals = $770.09       $832.6832   $832.68   $832.70   $832.60