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 $93.53   4.410%   $97.6547   $97.65   $97.65   $97.70  
  Purchase #2 $132.87   9.457%   $145.4355   $145.44   $145.45   $145.40  
  Purchase #3 $155.53   11.178%   $172.9151   $172.92   $172.90   $172.90  
  Purchase #4 $26.45   3.370%   $27.3414   $27.34   $27.35   $27.30  
  Purchase #5 $57.99   9.868%   $63.7125   $63.71   $63.70   $63.70  
  Purchase #6 $10.32   8.609%   $11.2084   $11.21   $11.20   $11.20  
  Purchase #7 $211.87   13.775%   $241.0551   $241.06   $241.05   $241.10  
  7 purchase totals = $688.56       $759.3227   $759.33   $759.30   $759.30