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 $71.70   5.856%   $75.8988   $75.90   $75.90   $75.90  
  Purchase #2 $184.44   6.500%   $196.4286   $196.43   $196.45   $196.40  
  Purchase #3 $228.25   7.550%   $245.4829   $245.48   $245.50   $245.50  
  Purchase #4 $158.54   5.663%   $167.5181   $167.52   $167.50   $167.50  
  Purchase #5 $116.43   8.332%   $126.1309   $126.13   $126.15   $126.10  
  Purchase #6 $52.87   6.812%   $56.4715   $56.47   $56.45   $56.50  
  Purchase #7 $5.54   9.572%   $6.0703   $6.07   $6.05   $6.10  
  7 purchase totals = $817.77       $874.0011   $874.00   $874.00   $874.00