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 $116.49   9.674%   $127.7592   $127.76   $127.75   $127.80  
  Purchase #2 $216.89   6.183%   $230.3003   $230.30   $230.30   $230.30  
  Purchase #3 $166.45   9.161%   $181.6985   $181.70   $181.70   $181.70  
  Purchase #4 $231.61   8.148%   $250.4816   $250.48   $250.50   $250.50  
  Purchase #5 $173.52   9.284%   $189.6296   $189.63   $189.65   $189.60  
  Purchase #6 $150.86   11.585%   $168.3371   $168.34   $168.35   $168.30  
  Purchase #7 $184.58   11.855%   $206.462   $206.46   $206.45   $206.50  
  7 purchase totals = $1,240.40       $1,354.6683   $1,354.67   $1,354.70   $1,354.70