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 $92.68   5.698%   $97.9609   $97.96   $97.95   $98.00  
  Purchase #2 $175.29   7.263%   $188.0213   $188.02   $188.00   $188.00  
  Purchase #3 $168.45   10.678%   $186.4371   $186.44   $186.45   $186.40  
  Purchase #4 $237.44   3.666%   $246.1446   $246.14   $246.15   $246.10  
  Purchase #5 $25.38   5.657%   $26.8157   $26.82   $26.80   $26.80  
  Purchase #6 $75.75   6.554%   $80.7147   $80.71   $80.70   $80.70  
  Purchase #7 $202.95   10.865%   $225.0005   $225.00   $225.00   $225.00  
  7 purchase totals = $977.94       $1,051.0948   $1,051.09   $1,051.05   $1,051.00