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 $52.40   6.269%   $55.685   $55.69   $55.70   $55.70  
  Purchase #2 $85.26   9.701%   $93.5311   $93.53   $93.55   $93.50  
  Purchase #3 $91.53   5.258%   $96.3426   $96.34   $96.35   $96.30  
  Purchase #4 $235.31   10.380%   $259.7352   $259.74   $259.75   $259.70  
  Purchase #5 $106.46   6.672%   $113.563   $113.56   $113.55   $113.60  
  Purchase #6 $71.72   5.498%   $75.6632   $75.66   $75.65   $75.70  
  Purchase #7 $218.67   3.103%   $225.4553   $225.46   $225.45   $225.50  
  7 purchase totals = $861.35       $919.9754   $919.98   $920.00   $920.00