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 $222.93   10.132%   $245.5173   $245.52   $245.50   $245.50  
  Purchase #2 $113.72   6.618%   $121.246   $121.25   $121.25   $121.20  
  Purchase #3 $49.33   11.175%   $54.8426   $54.84   $54.85   $54.80  
  Purchase #4 $204.62   9.432%   $223.9198   $223.92   $223.90   $223.90  
  Purchase #5 $156.52   11.323%   $174.2428   $174.24   $174.25   $174.20  
  Purchase #6 $119.98   3.309%   $123.9501   $123.95   $123.95   $124.00  
  Purchase #7 $7.74   3.269%   $7.993   $7.99   $8.00   $8.00  
  7 purchase totals = $874.84       $951.7116   $951.71   $951.70   $951.60