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 $56.56   11.413%   $63.0152   $63.02   $63.00   $63.00  
  Purchase #2 $93.87   3.407%   $97.0682   $97.07   $97.05   $97.10  
  Purchase #3 $153.77   12.372%   $172.7944   $172.79   $172.80   $172.80  
  Purchase #4 $18.45   12.627%   $20.7797   $20.78   $20.80   $20.80  
  Purchase #5 $75.97   13.171%   $85.976   $85.98   $86.00   $86.00  
  Purchase #6 $33.77   12.519%   $37.9977   $38.00   $38.00   $38.00  
  Purchase #7 $11.37   11.614%   $12.6905   $12.69   $12.70   $12.70  
  7 purchase totals = $443.76       $490.3217   $490.33   $490.35   $490.40