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 $206.65   13.106%   $233.7335   $233.73   $233.75   $233.70  
  Purchase #2 $197.52   3.688%   $204.8045   $204.80   $204.80   $204.80  
  Purchase #3 $98.47   11.866%   $110.1545   $110.15   $110.15   $110.20  
  Purchase #4 $224.45   5.144%   $235.9957   $236.00   $236.00   $236.00  
  Purchase #5 $141.39   6.138%   $150.0685   $150.07   $150.05   $150.10  
  Purchase #6 $11.52   6.389%   $12.256   $12.26   $12.25   $12.30  
  Purchase #7 $106.27   4.166%   $110.6972   $110.70   $110.70   $110.70  
  7 purchase totals = $986.27       $1,057.7099   $1,057.71   $1,057.70   $1,057.80