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 $48.84   12.348%   $54.8708   $54.87   $54.85   $54.90  
  Purchase #2 $195.50   5.538%   $206.3268   $206.33   $206.35   $206.30  
  Purchase #3 $224.58   9.573%   $246.079   $246.08   $246.10   $246.10  
  Purchase #4 $211.74   5.181%   $222.7102   $222.71   $222.70   $222.70  
  Purchase #5 $95.38   13.874%   $108.613   $108.61   $108.60   $108.60  
  Purchase #6 $199.81   8.370%   $216.5341   $216.53   $216.55   $216.50  
  Purchase #7 $159.82   13.485%   $181.3717   $181.37   $181.35   $181.40  
  7 purchase totals = $1,135.67       $1,236.5056   $1,236.50   $1,236.50   $1,236.50