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 $63.25   5.462%   $66.7047   $66.70   $66.70   $66.70  
  Purchase #2 $187.51   8.131%   $202.7564   $202.76   $202.75   $202.80  
  Purchase #3 $137.94   9.298%   $150.7657   $150.77   $150.75   $150.80  
  Purchase #4 $177.48   11.438%   $197.7802   $197.78   $197.80   $197.80  
  Purchase #5 $24.76   3.704%   $25.6771   $25.68   $25.70   $25.70  
  Purchase #6 $43.44   9.299%   $47.4795   $47.48   $47.50   $47.50  
  Purchase #7 $23.32   4.406%   $24.3475   $24.35   $24.35   $24.30  
  7 purchase totals = $657.70       $715.5111   $715.52   $715.55   $715.60