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 $63.29   3.111%   $65.259   $65.26   $65.25   $65.30  
  Purchase #2 $134.98   6.263%   $143.4338   $143.43   $143.45   $143.40  
  Purchase #3 $203.28   13.427%   $230.5744   $230.57   $230.55   $230.60  
  Purchase #4 $165.40   11.596%   $184.5798   $184.58   $184.60   $184.60  
  Purchase #5 $34.87   4.711%   $36.5127   $36.51   $36.50   $36.50  
  Purchase #6 $24.90   11.670%   $27.8058   $27.81   $27.80   $27.80  
  Purchase #7 $94.58   3.258%   $97.6614   $97.66   $97.65   $97.70  
  7 purchase totals = $721.30       $785.8269   $785.82   $785.80   $785.90