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 $116.47   6.271%   $123.7738   $123.77   $123.75   $123.80  
  Purchase #2 $86.29   10.353%   $95.2236   $95.22   $95.20   $95.20  
  Purchase #3 $67.52   4.310%   $70.4301   $70.43   $70.45   $70.40  
  Purchase #4 $190.93   3.412%   $197.4445   $197.44   $197.45   $197.40  
  Purchase #5 $10.97   7.625%   $11.8065   $11.81   $11.80   $11.80  
  Purchase #6 $203.41   3.294%   $210.1103   $210.11   $210.10   $210.10  
  Purchase #7 $120.99   4.494%   $126.4273   $126.43   $126.45   $126.40  
  7 purchase totals = $796.58       $835.2161   $835.21   $835.20   $835.10