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 $60.30   8.398%   $65.364   $65.36   $65.35   $65.40  
  Purchase #2 $48.58   6.371%   $51.675   $51.68   $51.70   $51.70  
  Purchase #3 $247.98   9.244%   $270.9033   $270.90   $270.90   $270.90  
  Purchase #4 $11.62   6.320%   $12.3544   $12.35   $12.35   $12.40  
  Purchase #5 $124.78   10.732%   $138.1714   $138.17   $138.15   $138.20  
  Purchase #6 $79.28   10.281%   $87.4308   $87.43   $87.45   $87.40  
  Purchase #7 $60.72   10.487%   $67.0877   $67.09   $67.10   $67.10  
  7 purchase totals = $633.26       $692.9866   $692.98   $693.00   $693.10