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 $168.79   12.843%   $190.4677   $190.47   $190.45   $190.50  
  Purchase #2 $81.68   4.719%   $85.5345   $85.53   $85.55   $85.50  
  Purchase #3 $155.86   13.830%   $177.4154   $177.42   $177.40   $177.40  
  Purchase #4 $33.43   9.155%   $36.4905   $36.49   $36.50   $36.50  
  Purchase #5 $234.74   6.756%   $250.599   $250.60   $250.60   $250.60  
  Purchase #6 $39.44   11.218%   $43.8644   $43.86   $43.85   $43.90  
  Purchase #7 $166.34   6.316%   $176.846   $176.85   $176.85   $176.80  
  7 purchase totals = $880.28       $961.2175   $961.22   $961.20   $961.20