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 $34.68   3.540%   $35.9077   $35.91   $35.90   $35.90  
  Purchase #2 $78.68   4.352%   $82.1042   $82.10   $82.10   $82.10  
  Purchase #3 $184.90   9.328%   $202.1475   $202.15   $202.15   $202.10  
  Purchase #4 $59.34   6.396%   $63.1354   $63.14   $63.15   $63.10  
  Purchase #5 $59.29   5.527%   $62.567   $62.57   $62.55   $62.60  
  Purchase #6 $229.52   3.285%   $237.0597   $237.06   $237.05   $237.10  
  Purchase #7 $160.44   9.104%   $175.0465   $175.05   $175.05   $175.00  
  7 purchase totals = $806.85       $857.9680   $857.98   $857.95   $857.90