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 $122.52   10.354%   $135.2057   $135.21   $135.20   $135.20  
  Purchase #2 $182.95   8.757%   $198.9709   $198.97   $198.95   $199.00  
  Purchase #3 $104.62   5.828%   $110.7173   $110.72   $110.70   $110.70  
  Purchase #4 $242.61   6.377%   $258.0812   $258.08   $258.10   $258.10  
  Purchase #5 $84.25   9.627%   $92.3607   $92.36   $92.35   $92.40  
  Purchase #6 $221.67   3.107%   $228.5573   $228.56   $228.55   $228.60  
  Purchase #7 $167.88   7.839%   $181.0401   $181.04   $181.05   $181.00  
  7 purchase totals = $1,126.50       $1,204.9332   $1,204.94   $1,204.90   $1,205.00