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 $202.64   7.436%   $217.7083   $217.71   $217.70   $217.70  
  Purchase #2 $171.92   13.817%   $195.6742   $195.67   $195.65   $195.70  
  Purchase #3 $241.99   9.173%   $264.1877   $264.19   $264.20   $264.20  
  Purchase #4 $156.58   9.451%   $171.3784   $171.38   $171.40   $171.40  
  Purchase #5 $41.28   6.735%   $44.0602   $44.06   $44.05   $44.10  
  Purchase #6 $108.67   12.764%   $122.5406   $122.54   $122.55   $122.50  
  Purchase #7 $79.90   10.387%   $88.1992   $88.20   $88.20   $88.20  
  7 purchase totals = $1,002.98       $1,103.7486   $1,103.75   $1,103.75   $1,103.80