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 $199.35   9.489%   $218.2663   $218.27   $218.25   $218.30  
  Purchase #2 $250.72   6.353%   $266.6482   $266.65   $266.65   $266.60  
  Purchase #3 $106.72   3.679%   $110.6462   $110.65   $110.65   $110.60  
  Purchase #4 $171.94   9.218%   $187.7894   $187.79   $187.80   $187.80  
  Purchase #5 $155.33   3.216%   $160.3254   $160.33   $160.35   $160.30  
  Purchase #6 $103.57   9.763%   $113.6815   $113.68   $113.70   $113.70  
  Purchase #7 $59.31   7.681%   $63.8656   $63.87   $63.85   $63.90  
  7 purchase totals = $1,046.94       $1,121.2226   $1,121.24   $1,121.25   $1,121.20