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 $222.91   8.704%   $242.3121   $242.31   $242.30   $242.30  
  Purchase #2 $6.33   7.278%   $6.7907   $6.79   $6.80   $6.80  
  Purchase #3 $99.63   11.373%   $110.9609   $110.96   $110.95   $111.00  
  Purchase #4 $160.61   3.695%   $166.5445   $166.54   $166.55   $166.50  
  Purchase #5 $122.97   6.687%   $131.193   $131.19   $131.20   $131.20  
  Purchase #6 $153.34   8.169%   $165.8663   $165.87   $165.85   $165.90  
  Purchase #7 $228.96   6.779%   $244.4812   $244.48   $244.50   $244.50  
  7 purchase totals = $994.75       $1,068.1487   $1,068.14   $1,068.15   $1,068.20