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 $108.33   9.285%   $118.3884   $118.39   $118.40   $118.40  
  Purchase #2 $130.49   11.746%   $145.8174   $145.82   $145.80   $145.80  
  Purchase #3 $160.63   12.702%   $181.0332   $181.03   $181.05   $181.00  
  Purchase #4 $115.62   9.328%   $126.405   $126.41   $126.40   $126.40  
  Purchase #5 $40.48   8.471%   $43.9091   $43.91   $43.90   $43.90  
  Purchase #6 $148.75   9.553%   $162.9601   $162.96   $162.95   $163.00  
  Purchase #7 $210.38   11.716%   $235.0281   $235.03   $235.05   $235.00  
  7 purchase totals = $914.68       $1,013.5413   $1,013.55   $1,013.55   $1,013.50