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 $61.53   5.852%   $65.1307   $65.13   $65.15   $65.10  
  Purchase #2 $236.88   9.506%   $259.3978   $259.40   $259.40   $259.40  
  Purchase #3 $185.91   12.836%   $209.7734   $209.77   $209.75   $209.80  
  Purchase #4 $71.96   7.841%   $77.6024   $77.60   $77.60   $77.60  
  Purchase #5 $152.39   8.254%   $164.9683   $164.97   $164.95   $165.00  
  Purchase #6 $95.45   12.260%   $107.1522   $107.15   $107.15   $107.20  
  Purchase #7 $201.83   7.398%   $216.7614   $216.76   $216.75   $216.80  
  7 purchase totals = $1,005.95       $1,100.7862   $1,100.78   $1,100.75   $1,100.90