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 $88.98   5.809%   $94.1488   $94.15   $94.15   $94.10  
  Purchase #2 $77.84   3.192%   $80.3247   $80.32   $80.30   $80.30  
  Purchase #3 $108.54   8.613%   $117.8886   $117.89   $117.90   $117.90  
  Purchase #4 $23.80   3.746%   $24.6915   $24.69   $24.70   $24.70  
  Purchase #5 $176.46   4.335%   $184.1095   $184.11   $184.10   $184.10  
  Purchase #6 $14.66   13.529%   $16.6434   $16.64   $16.65   $16.60  
  Purchase #7 $216.88   11.431%   $241.6716   $241.67   $241.65   $241.70  
  7 purchase totals = $707.16       $759.4781   $759.47   $759.45   $759.40