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 $106.96   11.853%   $119.638   $119.64   $119.65   $119.60  
  Purchase #2 $23.96   9.635%   $26.2685   $26.27   $26.25   $26.30  
  Purchase #3 $209.32   9.819%   $229.8731   $229.87   $229.85   $229.90  
  Purchase #4 $232.52   9.573%   $254.7791   $254.78   $254.80   $254.80  
  Purchase #5 $114.97   9.157%   $125.4978   $125.50   $125.50   $125.50  
  Purchase #6 $232.65   12.221%   $261.0822   $261.08   $261.10   $261.10  
  Purchase #7 $114.27   13.123%   $129.2657   $129.27   $129.25   $129.30  
  7 purchase totals = $1,034.65       $1,146.4044   $1,146.41   $1,146.40   $1,146.50