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 $62.84   12.310%   $70.5756   $70.58   $70.60   $70.60  
  Purchase #2 $223.25   10.519%   $246.7337   $246.73   $246.75   $246.70  
  Purchase #3 $165.37   4.670%   $173.0928   $173.09   $173.10   $173.10  
  Purchase #4 $145.99   5.369%   $153.8282   $153.83   $153.85   $153.80  
  Purchase #5 $59.88   12.285%   $67.2363   $67.24   $67.25   $67.20  
  Purchase #6 $123.77   11.365%   $137.8365   $137.84   $137.85   $137.80  
  Purchase #7 $171.37   3.785%   $177.8564   $177.86   $177.85   $177.90  
  7 purchase totals = $952.47       $1,027.1595   $1,027.17   $1,027.25   $1,027.10