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 $56.42   5.416%   $59.4757   $59.48   $59.50   $59.50  
  Purchase #2 $102.52   5.590%   $108.2509   $108.25   $108.25   $108.30  
  Purchase #3 $134.74   9.527%   $147.5767   $147.58   $147.60   $147.60  
  Purchase #4 $104.73   12.544%   $117.8673   $117.87   $117.85   $117.90  
  Purchase #5 $176.60   13.450%   $200.3527   $200.35   $200.35   $200.40  
  Purchase #6 $239.62   8.751%   $260.5891   $260.59   $260.60   $260.60  
  Purchase #7 $214.51   11.689%   $239.5841   $239.58   $239.60   $239.60  
  7 purchase totals = $1,029.14       $1,133.6965   $1,133.70   $1,133.75   $1,133.90