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 $66.81   4.766%   $69.9942   $69.99   $70.00   $70.00  
  Purchase #2 $160.36   13.368%   $181.7969   $181.80   $181.80   $181.80  
  Purchase #3 $155.63   4.630%   $162.8357   $162.84   $162.85   $162.80  
  Purchase #4 $24.34   6.657%   $25.9603   $25.96   $25.95   $26.00  
  Purchase #5 $123.36   3.580%   $127.7763   $127.78   $127.80   $127.80  
  Purchase #6 $61.92   8.522%   $67.1968   $67.20   $67.20   $67.20  
  Purchase #7 $202.93   11.516%   $226.2994   $226.30   $226.30   $226.30  
  7 purchase totals = $795.35       $861.8596   $861.87   $861.90   $861.90