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 $113.42   9.355%   $124.0304   $124.03   $124.05   $124.00  
  Purchase #2 $158.72   10.221%   $174.9428   $174.94   $174.95   $174.90  
  Purchase #3 $17.62   9.666%   $19.3231   $19.32   $19.30   $19.30  
  Purchase #4 $245.26   7.829%   $264.4614   $264.46   $264.45   $264.50  
  Purchase #5 $110.87   8.109%   $119.8604   $119.86   $119.85   $119.90  
  Purchase #6 $210.40   12.445%   $236.5843   $236.58   $236.60   $236.60  
  Purchase #7 $74.44   10.604%   $82.3336   $82.33   $82.35   $82.30  
  7 purchase totals = $930.73       $1,021.5360   $1,021.52   $1,021.55   $1,021.50