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 $24.38   6.503%   $25.9654   $25.97   $25.95   $26.00  
  Purchase #2 $230.46   7.488%   $247.7168   $247.72   $247.70   $247.70  
  Purchase #3 $137.52   9.709%   $150.8718   $150.87   $150.85   $150.90  
  Purchase #4 $136.25   6.804%   $145.5205   $145.52   $145.50   $145.50  
  Purchase #5 $66.78   4.557%   $69.8232   $69.82   $69.80   $69.80  
  Purchase #6 $230.57   4.618%   $241.2177   $241.22   $241.20   $241.20  
  Purchase #7 $127.89   9.616%   $140.1879   $140.19   $140.20   $140.20  
  7 purchase totals = $953.85       $1,021.3033   $1,021.31   $1,021.20   $1,021.30