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 $173.34   6.565%   $184.7198   $184.72   $184.70   $184.70  
  Purchase #2 $149.95   11.352%   $166.9723   $166.97   $166.95   $167.00  
  Purchase #3 $23.43   6.187%   $24.8796   $24.88   $24.90   $24.90  
  Purchase #4 $51.37   10.352%   $56.6878   $56.69   $56.70   $56.70  
  Purchase #5 $91.30   6.621%   $97.345   $97.35   $97.35   $97.30  
  Purchase #6 $226.42   5.604%   $239.1086   $239.11   $239.10   $239.10  
  Purchase #7 $86.50   6.572%   $92.1848   $92.18   $92.20   $92.20  
  7 purchase totals = $802.31       $861.8979   $861.90   $861.90   $861.90