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 $92.47   3.481%   $95.6889   $95.69   $95.70   $95.70  
  Purchase #2 $72.86   5.676%   $76.9955   $77.00   $77.00   $77.00  
  Purchase #3 $239.44   8.798%   $260.5059   $260.51   $260.50   $260.50  
  Purchase #4 $22.67   8.308%   $24.5534   $24.55   $24.55   $24.60  
  Purchase #5 $97.44   6.592%   $103.8632   $103.86   $103.85   $103.90  
  Purchase #6 $194.53   9.290%   $212.6018   $212.60   $212.60   $212.60  
  Purchase #7 $115.52   11.486%   $128.7886   $128.79   $128.80   $128.80  
  7 purchase totals = $834.93       $902.9973   $903.00   $903.00   $903.10