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 $86.36   11.356%   $96.167   $96.17   $96.15   $96.20  
  Purchase #2 $99.78   3.178%   $102.951   $102.95   $102.95   $103.00  
  Purchase #3 $194.82   6.614%   $207.7054   $207.71   $207.70   $207.70  
  Purchase #4 $204.99   4.674%   $214.5712   $214.57   $214.55   $214.60  
  Purchase #5 $62.78   12.400%   $70.5647   $70.56   $70.55   $70.60  
  Purchase #6 $55.55   3.672%   $57.5898   $57.59   $57.60   $57.60  
  Purchase #7 $26.80   5.781%   $28.3493   $28.35   $28.35   $28.30  
  7 purchase totals = $731.08       $777.8984   $777.90   $777.85   $778.00