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 $118.96   4.672%   $124.5178   $124.52   $124.50   $124.50  
  Purchase #2 $119.44   10.147%   $131.5596   $131.56   $131.55   $131.60  
  Purchase #3 $113.26   11.845%   $126.6756   $126.68   $126.70   $126.70  
  Purchase #4 $116.57   11.706%   $130.2157   $130.22   $130.20   $130.20  
  Purchase #5 $160.46   3.119%   $165.4647   $165.46   $165.45   $165.50  
  Purchase #6 $100.27   13.586%   $113.8927   $113.89   $113.90   $113.90  
  Purchase #7 $188.30   3.186%   $194.2992   $194.30   $194.30   $194.30  
  7 purchase totals = $917.26       $986.6253   $986.63   $986.60   $986.70