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 $48.61   11.428%   $54.1652   $54.17   $54.15   $54.20  
  Purchase #2 $119.64   9.147%   $130.5835   $130.58   $130.60   $130.60  
  Purchase #3 $165.57   9.301%   $180.9697   $180.97   $180.95   $181.00  
  Purchase #4 $226.81   6.556%   $241.6797   $241.68   $241.70   $241.70  
  Purchase #5 $135.39   11.759%   $151.3105   $151.31   $151.30   $151.30  
  Purchase #6 $247.86   7.389%   $266.1744   $266.17   $266.15   $266.20  
  Purchase #7 $211.59   7.279%   $226.9916   $226.99   $227.00   $227.00  
  7 purchase totals = $1,155.47       $1,251.8746   $1,251.87   $1,251.85   $1,252.00