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 $113.31   9.187%   $123.7198   $123.72   $123.70   $123.70  
  Purchase #2 $5.25   12.481%   $5.9053   $5.91   $5.90   $5.90  
  Purchase #3 $42.82   11.191%   $47.612   $47.61   $47.60   $47.60  
  Purchase #4 $23.76   11.265%   $26.4366   $26.44   $26.45   $26.40  
  Purchase #5 $249.40   9.594%   $273.3274   $273.33   $273.35   $273.30  
  Purchase #6 $158.84   4.207%   $165.5224   $165.52   $165.50   $165.50  
  Purchase #7 $57.96   3.480%   $59.977   $59.98   $60.00   $60.00  
  7 purchase totals = $651.34       $702.5005   $702.51   $702.50   $702.40