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 $129.68   5.519%   $136.837   $136.84   $136.85   $136.80  
  Purchase #2 $206.32   13.628%   $234.4373   $234.44   $234.45   $234.40  
  Purchase #3 $29.55   5.545%   $31.1885   $31.19   $31.20   $31.20  
  Purchase #4 $114.67   8.466%   $124.378   $124.38   $124.40   $124.40  
  Purchase #5 $179.98   8.871%   $195.946   $195.95   $195.95   $195.90  
  Purchase #6 $226.28   8.428%   $245.3509   $245.35   $245.35   $245.40  
  Purchase #7 $182.29   8.424%   $197.6461   $197.65   $197.65   $197.60  
  7 purchase totals = $1,068.77       $1,165.7838   $1,165.80   $1,165.85   $1,165.70