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 $141.66   8.701%   $153.9858   $153.99   $154.00   $154.00  
  Purchase #2 $31.72   12.169%   $35.58   $35.58   $35.60   $35.60  
  Purchase #3 $151.46   12.577%   $170.5091   $170.51   $170.50   $170.50  
  Purchase #4 $32.95   9.755%   $36.1643   $36.16   $36.15   $36.20  
  Purchase #5 $103.94   6.358%   $110.5485   $110.55   $110.55   $110.50  
  Purchase #6 $172.93   6.502%   $184.1739   $184.17   $184.15   $184.20  
  Purchase #7 $235.84   10.332%   $260.207   $260.21   $260.20   $260.20  
  7 purchase totals = $870.50       $951.1686   $951.17   $951.15   $951.20