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 $218.41   10.650%   $241.6707   $241.67   $241.65   $241.70  
  Purchase #2 $149.33   8.253%   $161.6542   $161.65   $161.65   $161.70  
  Purchase #3 $246.41   3.826%   $255.8376   $255.84   $255.85   $255.80  
  Purchase #4 $163.93   10.843%   $181.7049   $181.70   $181.70   $181.70  
  Purchase #5 $204.63   13.803%   $232.8751   $232.88   $232.90   $232.90  
  Purchase #6 $165.70   12.744%   $186.8168   $186.82   $186.80   $186.80  
  Purchase #7 $17.97   4.753%   $18.8241   $18.82   $18.80   $18.80  
  7 purchase totals = $1,166.38       $1,279.3834   $1,279.38   $1,279.35   $1,279.40