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 $54.58   11.170%   $60.6766   $60.68   $60.70   $60.70  
  Purchase #2 $135.31   5.636%   $142.9361   $142.94   $142.95   $142.90  
  Purchase #3 $91.64   9.196%   $100.0672   $100.07   $100.05   $100.10  
  Purchase #4 $165.36   11.856%   $184.9651   $184.97   $184.95   $185.00  
  Purchase #5 $190.69   5.815%   $201.7786   $201.78   $201.80   $201.80  
  Purchase #6 $59.93   3.263%   $61.8855   $61.89   $61.90   $61.90  
  Purchase #7 $21.96   13.809%   $24.9925   $24.99   $25.00   $25.00  
  7 purchase totals = $719.47       $777.3016   $777.32   $777.35   $777.40