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 $51.50   13.740%   $58.5761   $58.58   $58.60   $58.60  
  Purchase #2 $231.77   9.858%   $254.6179   $254.62   $254.60   $254.60  
  Purchase #3 $150.62   13.227%   $170.5425   $170.54   $170.55   $170.50  
  Purchase #4 $27.40   6.540%   $29.192   $29.19   $29.20   $29.20  
  Purchase #5 $240.45   9.564%   $263.4466   $263.45   $263.45   $263.40  
  Purchase #6 $62.49   7.543%   $67.2036   $67.20   $67.20   $67.20  
  Purchase #7 $176.63   3.761%   $183.2731   $183.27   $183.25   $183.30  
  7 purchase totals = $940.86       $1,026.8518   $1,026.85   $1,026.85   $1,026.80