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 $184.94   9.382%   $202.2911   $202.29   $202.30   $202.30  
  Purchase #2 $185.40   13.174%   $209.8246   $209.82   $209.80   $209.80  
  Purchase #3 $120.32   3.740%   $124.82   $124.82   $124.80   $124.80  
  Purchase #4 $56.33   12.446%   $63.3408   $63.34   $63.35   $63.30  
  Purchase #5 $169.50   13.543%   $192.4554   $192.46   $192.45   $192.50  
  Purchase #6 $206.43   13.590%   $234.4838   $234.48   $234.50   $234.50  
  Purchase #7 $160.50   11.460%   $178.8933   $178.89   $178.90   $178.90  
  7 purchase totals = $1,083.42       $1,206.1090   $1,206.10   $1,206.10   $1,206.10