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 $42.52   12.102%   $47.6658   $47.67   $47.65   $47.70  
  Purchase #2 $156.74   12.191%   $175.8482   $175.85   $175.85   $175.80  
  Purchase #3 $197.83   3.162%   $204.0854   $204.09   $204.10   $204.10  
  Purchase #4 $110.55   10.796%   $122.485   $122.49   $122.50   $122.50  
  Purchase #5 $126.40   4.298%   $131.8327   $131.83   $131.85   $131.80  
  Purchase #6 $162.33   9.156%   $177.1929   $177.19   $177.20   $177.20  
  Purchase #7 $141.41   11.441%   $157.5887   $157.59   $157.60   $157.60  
  7 purchase totals = $937.78       $1,016.6987   $1,016.71   $1,016.75   $1,016.70