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 $246.46   8.677%   $267.8453   $267.85   $267.85   $267.80  
  Purchase #2 $109.70   13.125%   $124.0981   $124.10   $124.10   $124.10  
  Purchase #3 $30.43   10.662%   $33.6744   $33.67   $33.65   $33.70  
  Purchase #4 $35.30   11.563%   $39.3817   $39.38   $39.40   $39.40  
  Purchase #5 $89.62   6.701%   $95.6254   $95.63   $95.65   $95.60  
  Purchase #6 $38.41   12.367%   $43.1602   $43.16   $43.15   $43.20  
  Purchase #7 $147.32   3.676%   $152.7355   $152.74   $152.75   $152.70  
  7 purchase totals = $697.24       $756.5206   $756.53   $756.55   $756.50