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 $56.56   7.620%   $60.8699   $60.87   $60.85   $60.90  
  Purchase #2 $126.88   12.731%   $143.0331   $143.03   $143.05   $143.00  
  Purchase #3 $135.89   5.213%   $142.9739   $142.97   $142.95   $143.00  
  Purchase #4 $232.77   13.613%   $264.457   $264.46   $264.45   $264.50  
  Purchase #5 $22.95   12.742%   $25.8743   $25.87   $25.85   $25.90  
  Purchase #6 $250.86   7.243%   $269.0298   $269.03   $269.05   $269.00  
  Purchase #7 $73.31   11.389%   $81.6593   $81.66   $81.65   $81.70  
  7 purchase totals = $899.22       $987.8973   $987.89   $987.85   $988.00