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 $24.25   11.468%   $27.031   $27.03   $27.05   $27.00  
  Purchase #2 $214.98   3.171%   $221.797   $221.80   $221.80   $221.80  
  Purchase #3 $55.53   6.386%   $59.0761   $59.08   $59.10   $59.10  
  Purchase #4 $71.70   5.474%   $75.6249   $75.62   $75.60   $75.60  
  Purchase #5 $9.75   8.400%   $10.569   $10.57   $10.55   $10.60  
  Purchase #6 $110.43   13.510%   $125.3491   $125.35   $125.35   $125.30  
  Purchase #7 $243.79   6.668%   $260.0459   $260.05   $260.05   $260.00  
  7 purchase totals = $730.43       $779.4930   $779.50   $779.50   $779.40