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 $182.70   10.421%   $201.7392   $201.74   $201.75   $201.70  
  Purchase #2 $35.68   8.693%   $38.7817   $38.78   $38.80   $38.80  
  Purchase #3 $73.50   13.770%   $83.621   $83.62   $83.60   $83.60  
  Purchase #4 $239.27   10.270%   $263.843   $263.84   $263.85   $263.80  
  Purchase #5 $90.72   3.822%   $94.1873   $94.19   $94.20   $94.20  
  Purchase #6 $171.96   6.735%   $183.5415   $183.54   $183.55   $183.50  
  Purchase #7 $189.43   12.639%   $213.3721   $213.37   $213.35   $213.40  
  7 purchase totals = $983.26       $1,079.0858   $1,079.08   $1,079.10   $1,079.00