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 $53.45   10.231%   $58.9185   $58.92   $58.90   $58.90  
  Purchase #2 $47.40   3.360%   $48.9926   $48.99   $49.00   $49.00  
  Purchase #3 $104.39   13.422%   $118.4012   $118.40   $118.40   $118.40  
  Purchase #4 $187.80   12.351%   $210.9952   $211.00   $211.00   $211.00  
  Purchase #5 $201.92   8.187%   $218.4512   $218.45   $218.45   $218.50  
  Purchase #6 $225.92   6.704%   $241.0657   $241.07   $241.05   $241.10  
  Purchase #7 $104.93   12.415%   $117.9571   $117.96   $117.95   $118.00  
  7 purchase totals = $925.81       $1,014.7815   $1,014.79   $1,014.75   $1,014.90