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 $152.44   9.768%   $167.3303   $167.33   $167.35   $167.30  
  Purchase #2 $32.65   11.242%   $36.3205   $36.32   $36.30   $36.30  
  Purchase #3 $132.45   7.271%   $142.0804   $142.08   $142.10   $142.10  
  Purchase #4 $167.80   8.731%   $182.4506   $182.45   $182.45   $182.50  
  Purchase #5 $201.53   11.433%   $224.5709   $224.57   $224.55   $224.60  
  Purchase #6 $124.58   3.699%   $129.1882   $129.19   $129.20   $129.20  
  Purchase #7 $118.35   8.489%   $128.3967   $128.40   $128.40   $128.40  
  7 purchase totals = $929.80       $1,010.3376   $1,010.34   $1,010.35   $1,010.40