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 $53.32   10.353%   $58.8402   $58.84   $58.85   $58.80  
  Purchase #2 $240.29   5.310%   $253.0494   $253.05   $253.05   $253.00  
  Purchase #3 $26.93   10.536%   $29.7673   $29.77   $29.75   $29.80  
  Purchase #4 $245.32   10.554%   $271.2111   $271.21   $271.20   $271.20  
  Purchase #5 $53.95   8.542%   $58.5584   $58.56   $58.55   $58.60  
  Purchase #6 $152.92   12.410%   $171.8974   $171.90   $171.90   $171.90  
  Purchase #7 $247.42   11.718%   $276.4127   $276.41   $276.40   $276.40  
  7 purchase totals = $1,020.15       $1,119.7365   $1,119.74   $1,119.70   $1,119.70