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 $106.31   6.363%   $113.0745   $113.07   $113.05   $113.10  
  Purchase #2 $118.77   13.396%   $134.6804   $134.68   $134.70   $134.70  
  Purchase #3 $54.77   11.754%   $61.2077   $61.21   $61.20   $61.20  
  Purchase #4 $232.28   3.262%   $239.857   $239.86   $239.85   $239.90  
  Purchase #5 $20.58   6.644%   $21.9473   $21.95   $21.95   $21.90  
  Purchase #6 $194.97   3.626%   $202.0396   $202.04   $202.05   $202.00  
  Purchase #7 $190.49   6.589%   $203.0414   $203.04   $203.05   $203.00  
  7 purchase totals = $918.17       $975.8479   $975.85   $975.85   $975.80