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 $247.39   6.688%   $263.9354   $263.94   $263.95   $263.90  
  Purchase #2 $149.82   10.364%   $165.3473   $165.35   $165.35   $165.30  
  Purchase #3 $109.87   6.669%   $117.1972   $117.20   $117.20   $117.20  
  Purchase #4 $241.34   7.807%   $260.1814   $260.18   $260.20   $260.20  
  Purchase #5 $61.29   12.456%   $68.9243   $68.92   $68.90   $68.90  
  Purchase #6 $200.57   5.387%   $211.3747   $211.37   $211.35   $211.40  
  Purchase #7 $185.94   13.563%   $211.159   $211.16   $211.15   $211.20  
  7 purchase totals = $1,196.22       $1,298.1193   $1,298.12   $1,298.10   $1,298.10