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 $179.63   12.597%   $202.258   $202.26   $202.25   $202.30  
  Purchase #2 $6.46   7.652%   $6.9543   $6.95   $6.95   $7.00  
  Purchase #3 $74.47   4.256%   $77.6394   $77.64   $77.65   $77.60  
  Purchase #4 $162.52   9.460%   $177.8944   $177.89   $177.90   $177.90  
  Purchase #5 $237.49   11.382%   $264.5211   $264.52   $264.50   $264.50  
  Purchase #6 $231.32   6.497%   $246.3489   $246.35   $246.35   $246.30  
  Purchase #7 $36.35   6.620%   $38.7564   $38.76   $38.75   $38.80  
  7 purchase totals = $928.24       $1,014.3725   $1,014.37   $1,014.35   $1,014.40