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 $67.62   11.671%   $75.5119   $75.51   $75.50   $75.50  
  Purchase #2 $104.75   3.324%   $108.2319   $108.23   $108.25   $108.20  
  Purchase #3 $120.56   12.505%   $135.636   $135.64   $135.65   $135.60  
  Purchase #4 $162.69   3.787%   $168.8511   $168.85   $168.85   $168.90  
  Purchase #5 $191.48   6.230%   $203.4092   $203.41   $203.40   $203.40  
  Purchase #6 $65.35   9.678%   $71.6746   $71.67   $71.65   $71.70  
  Purchase #7 $66.65   3.493%   $68.9781   $68.98   $69.00   $69.00  
  7 purchase totals = $779.10       $832.2928   $832.29   $832.30   $832.30