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 $56.85   3.184%   $58.6601   $58.66   $58.65   $58.70  
  Purchase #2 $108.32   10.196%   $119.3643   $119.36   $119.35   $119.40  
  Purchase #3 $8.89   13.378%   $10.0793   $10.08   $10.10   $10.10  
  Purchase #4 $108.36   13.255%   $122.7231   $122.72   $122.70   $122.70  
  Purchase #5 $205.31   13.232%   $232.4766   $232.48   $232.50   $232.50  
  Purchase #6 $209.79   5.548%   $221.4291   $221.43   $221.45   $221.40  
  Purchase #7 $236.36   9.467%   $258.7362   $258.74   $258.75   $258.70  
  7 purchase totals = $933.88       $1,023.4687   $1,023.47   $1,023.50   $1,023.50