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 $217.81   8.679%   $236.7137   $236.71   $236.70   $236.70  
  Purchase #2 $156.95   11.484%   $174.9741   $174.97   $174.95   $175.00  
  Purchase #3 $241.74   6.642%   $257.7964   $257.80   $257.80   $257.80  
  Purchase #4 $15.73   9.613%   $17.2421   $17.24   $17.25   $17.20  
  Purchase #5 $55.92   6.550%   $59.5828   $59.58   $59.60   $59.60  
  Purchase #6 $193.85   6.835%   $207.0996   $207.10   $207.10   $207.10  
  Purchase #7 $144.98   3.518%   $150.0804   $150.08   $150.10   $150.10  
  7 purchase totals = $1,026.98       $1,103.4891   $1,103.48   $1,103.50   $1,103.50