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 $126.80   5.699%   $134.0263   $134.03   $134.05   $134.00  
  Purchase #2 $54.78   3.109%   $56.4831   $56.48   $56.50   $56.50  
  Purchase #3 $61.47   13.198%   $69.5828   $69.58   $69.60   $69.60  
  Purchase #4 $189.76   7.386%   $203.7757   $203.78   $203.80   $203.80  
  Purchase #5 $230.29   8.141%   $249.0379   $249.04   $249.05   $249.00  
  Purchase #6 $135.38   5.761%   $143.1792   $143.18   $143.20   $143.20  
  Purchase #7 $240.50   11.517%   $268.1984   $268.20   $268.20   $268.20  
  7 purchase totals = $1,038.98       $1,124.2834   $1,124.29   $1,124.40   $1,124.30