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 $80.79   6.656%   $86.1674   $86.17   $86.15   $86.20  
  Purchase #2 $229.84   7.514%   $247.1102   $247.11   $247.10   $247.10  
  Purchase #3 $124.32   7.328%   $133.4302   $133.43   $133.45   $133.40  
  Purchase #4 $38.87   5.519%   $41.0152   $41.02   $41.00   $41.00  
  Purchase #5 $172.69   8.151%   $186.766   $186.77   $186.75   $186.80  
  Purchase #6 $9.75   12.575%   $10.9761   $10.98   $11.00   $11.00  
  Purchase #7 $233.49   5.481%   $246.2876   $246.29   $246.30   $246.30  
  7 purchase totals = $889.75       $951.7527   $951.77   $951.75   $951.80