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 $26.27   11.356%   $29.2532   $29.25   $29.25   $29.30  
  Purchase #2 $236.25   13.103%   $267.2058   $267.21   $267.20   $267.20  
  Purchase #3 $8.70   5.298%   $9.1609   $9.16   $9.15   $9.20  
  Purchase #4 $155.58   8.290%   $168.4776   $168.48   $168.50   $168.50  
  Purchase #5 $212.87   10.520%   $235.2639   $235.26   $235.25   $235.30  
  Purchase #6 $179.49   13.829%   $204.3117   $204.31   $204.30   $204.30  
  Purchase #7 $175.49   4.751%   $183.8275   $183.83   $183.85   $183.80  
  7 purchase totals = $994.65       $1,097.5006   $1,097.50   $1,097.50   $1,097.60