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 $173.45   10.273%   $191.2685   $191.27   $191.25   $191.30  
  Purchase #2 $53.70   9.786%   $58.9551   $58.96   $58.95   $59.00  
  Purchase #3 $134.99   6.380%   $143.6024   $143.60   $143.60   $143.60  
  Purchase #4 $69.86   6.722%   $74.556   $74.56   $74.55   $74.60  
  Purchase #5 $212.73   10.363%   $234.7752   $234.78   $234.80   $234.80  
  Purchase #6 $65.73   9.566%   $72.0177   $72.02   $72.00   $72.00  
  Purchase #7 $245.62   11.104%   $272.8936   $272.89   $272.90   $272.90  
  7 purchase totals = $956.08       $1,048.0685   $1,048.08   $1,048.05   $1,048.20