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 $68.65   8.293%   $74.3431   $74.34   $74.35   $74.30  
  Purchase #2 $246.90   13.123%   $279.3007   $279.30   $279.30   $279.30  
  Purchase #3 $248.80   7.103%   $266.4723   $266.47   $266.45   $266.50  
  Purchase #4 $146.59   3.327%   $151.467   $151.47   $151.45   $151.50  
  Purchase #5 $42.85   11.124%   $47.6166   $47.62   $47.60   $47.60  
  Purchase #6 $26.40   3.428%   $27.305   $27.31   $27.30   $27.30  
  Purchase #7 $232.36   5.464%   $245.0562   $245.06   $245.05   $245.10  
  7 purchase totals = $1,012.55       $1,091.5609   $1,091.57   $1,091.50   $1,091.60