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 $53.73   9.784%   $58.9869   $58.99   $59.00   $59.00  
  Purchase #2 $150.86   9.740%   $165.5538   $165.55   $165.55   $165.60  
  Purchase #3 $171.91   10.829%   $190.5261   $190.53   $190.55   $190.50  
  Purchase #4 $138.58   11.829%   $154.9726   $154.97   $154.95   $155.00  
  Purchase #5 $59.60   12.681%   $67.1579   $67.16   $67.15   $67.20  
  Purchase #6 $242.45   4.618%   $253.6463   $253.65   $253.65   $253.60  
  Purchase #7 $170.37   9.279%   $186.1786   $186.18   $186.20   $186.20  
  7 purchase totals = $987.50       $1,077.0222   $1,077.03   $1,077.05   $1,077.10