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 $65.62   11.240%   $72.9957   $73.00   $73.00   $73.00  
  Purchase #2 $43.79   3.823%   $45.4641   $45.46   $45.45   $45.50  
  Purchase #3 $230.75   5.343%   $243.079   $243.08   $243.10   $243.10  
  Purchase #4 $57.30   9.756%   $62.8902   $62.89   $62.90   $62.90  
  Purchase #5 $131.53   7.691%   $141.646   $141.65   $141.65   $141.60  
  Purchase #6 $246.60   10.212%   $271.7828   $271.78   $271.80   $271.80  
  Purchase #7 $222.39   10.583%   $245.9255   $245.93   $245.95   $245.90  
  7 purchase totals = $997.98       $1,083.7833   $1,083.79   $1,083.85   $1,083.80