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 $181.56   11.332%   $202.1344   $202.13   $202.15   $202.10  
  Purchase #2 $171.55   11.820%   $191.8272   $191.83   $191.85   $191.80  
  Purchase #3 $136.52   13.742%   $155.2806   $155.28   $155.30   $155.30  
  Purchase #4 $69.55   9.259%   $75.9896   $75.99   $76.00   $76.00  
  Purchase #5 $91.63   3.507%   $94.8435   $94.84   $94.85   $94.80  
  Purchase #6 $191.44   5.841%   $202.622   $202.62   $202.60   $202.60  
  Purchase #7 $117.77   3.836%   $122.2877   $122.29   $122.30   $122.30  
  7 purchase totals = $960.02       $1,044.9850   $1,044.98   $1,045.05   $1,044.90