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 $74.33   8.511%   $80.6562   $80.66   $80.65   $80.70  
  Purchase #2 $232.62   12.352%   $261.3532   $261.35   $261.35   $261.40  
  Purchase #3 $63.40   7.195%   $67.9616   $67.96   $67.95   $68.00  
  Purchase #4 $204.77   4.416%   $213.8126   $213.81   $213.80   $213.80  
  Purchase #5 $88.68   7.831%   $95.6245   $95.62   $95.60   $95.60  
  Purchase #6 $167.67   10.525%   $185.3173   $185.32   $185.30   $185.30  
  Purchase #7 $116.30   10.317%   $128.2987   $128.30   $128.30   $128.30  
  7 purchase totals = $947.77       $1,033.0241   $1,033.02   $1,032.95   $1,033.10