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 $162.48   5.815%   $171.9282   $171.93   $171.95   $171.90  
  Purchase #2 $22.33   7.737%   $24.0577   $24.06   $24.05   $24.10  
  Purchase #3 $103.94   6.363%   $110.5537   $110.55   $110.55   $110.60  
  Purchase #4 $188.88   7.629%   $203.2897   $203.29   $203.30   $203.30  
  Purchase #5 $132.57   10.489%   $146.4753   $146.48   $146.50   $146.50  
  Purchase #6 $225.29   10.255%   $248.3935   $248.39   $248.40   $248.40  
  Purchase #7 $83.86   11.171%   $93.228   $93.23   $93.25   $93.20  
  7 purchase totals = $919.35       $997.9261   $997.93   $998.00   $998.00