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 $204.33   6.319%   $217.2416   $217.24   $217.25   $217.20  
  Purchase #2 $178.58   5.132%   $187.7447   $187.74   $187.75   $187.70  
  Purchase #3 $65.65   12.585%   $73.9121   $73.91   $73.90   $73.90  
  Purchase #4 $211.85   12.253%   $237.808   $237.81   $237.80   $237.80  
  Purchase #5 $153.86   6.228%   $163.4424   $163.44   $163.45   $163.40  
  Purchase #6 $190.98   6.861%   $204.0831   $204.08   $204.10   $204.10  
  Purchase #7 $143.50   12.392%   $161.2825   $161.28   $161.30   $161.30  
  7 purchase totals = $1,148.75       $1,245.5144   $1,245.50   $1,245.55   $1,245.40