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 $41.51   13.290%   $47.0267   $47.03   $47.05   $47.00  
  Purchase #2 $81.57   12.129%   $91.4636   $91.46   $91.45   $91.50  
  Purchase #3 $88.82   4.369%   $92.7005   $92.70   $92.70   $92.70  
  Purchase #4 $239.82   9.311%   $262.1496   $262.15   $262.15   $262.10  
  Purchase #5 $127.81   6.774%   $136.4678   $136.47   $136.45   $136.50  
  Purchase #6 $181.54   9.341%   $198.4977   $198.50   $198.50   $198.50  
  Purchase #7 $205.56   7.410%   $220.792   $220.79   $220.80   $220.80  
  7 purchase totals = $966.63       $1,049.0979   $1,049.10   $1,049.10   $1,049.10