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 $59.92   8.530%   $65.0312   $65.03   $65.05   $65.00  
  Purchase #2 $11.45   6.617%   $12.2076   $12.21   $12.20   $12.20  
  Purchase #3 $203.44   4.539%   $212.6741   $212.67   $212.65   $212.70  
  Purchase #4 $19.25   7.592%   $20.7115   $20.71   $20.70   $20.70  
  Purchase #5 $155.41   7.467%   $167.0145   $167.01   $167.00   $167.00  
  Purchase #6 $209.83   7.834%   $226.2681   $226.27   $226.25   $226.30  
  Purchase #7 $37.34   4.595%   $39.0558   $39.06   $39.05   $39.10  
  7 purchase totals = $696.64       $742.9628   $742.96   $742.90   $743.00