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 $177.89   8.806%   $193.555   $193.56   $193.55   $193.60  
  Purchase #2 $209.43   12.534%   $235.68   $235.68   $235.70   $235.70  
  Purchase #3 $80.68   5.684%   $85.2659   $85.27   $85.25   $85.30  
  Purchase #4 $78.75   7.620%   $84.7508   $84.75   $84.75   $84.80  
  Purchase #5 $128.97   4.329%   $134.5531   $134.55   $134.55   $134.60  
  Purchase #6 $73.55   8.562%   $79.8474   $79.85   $79.85   $79.80  
  Purchase #7 $222.26   13.362%   $251.9584   $251.96   $251.95   $252.00  
  7 purchase totals = $971.53       $1,065.6106   $1,065.62   $1,065.60   $1,065.80