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 $80.91   13.704%   $91.9979   $92.00   $92.00   $92.00  
  Purchase #2 $24.59   6.575%   $26.2068   $26.21   $26.20   $26.20  
  Purchase #3 $220.25   13.195%   $249.312   $249.31   $249.30   $249.30  
  Purchase #4 $61.53   13.706%   $69.9633   $69.96   $69.95   $70.00  
  Purchase #5 $84.84   5.623%   $89.6106   $89.61   $89.60   $89.60  
  Purchase #6 $233.66   12.580%   $263.0544   $263.05   $263.05   $263.10  
  Purchase #7 $209.85   12.785%   $236.6793   $236.68   $236.70   $236.70  
  7 purchase totals = $915.63       $1,026.8243   $1,026.82   $1,026.80   $1,026.90