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 $241.88   9.398%   $264.6119   $264.61   $264.60   $264.60  
  Purchase #2 $163.96   8.473%   $177.8523   $177.85   $177.85   $177.90  
  Purchase #3 $84.70   12.645%   $95.4103   $95.41   $95.40   $95.40  
  Purchase #4 $133.72   4.249%   $139.4018   $139.40   $139.40   $139.40  
  Purchase #5 $239.56   5.162%   $251.9261   $251.93   $251.95   $251.90  
  Purchase #6 $163.95   5.150%   $172.3934   $172.39   $172.40   $172.40  
  Purchase #7 $120.50   6.319%   $128.1144   $128.11   $128.10   $128.10  
  7 purchase totals = $1,148.27       $1,229.7102   $1,229.70   $1,229.70   $1,229.70