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 $152.88   3.228%   $157.815   $157.82   $157.80   $157.80  
  Purchase #2 $164.33   7.727%   $177.0278   $177.03   $177.05   $177.00  
  Purchase #3 $48.59   11.112%   $53.9893   $53.99   $54.00   $54.00  
  Purchase #4 $32.83   8.117%   $35.4948   $35.49   $35.50   $35.50  
  Purchase #5 $176.87   8.317%   $191.5803   $191.58   $191.60   $191.60  
  Purchase #6 $172.86   11.663%   $193.0207   $193.02   $193.00   $193.00  
  Purchase #7 $24.74   10.582%   $27.358   $27.36   $27.35   $27.40  
  7 purchase totals = $773.10       $836.2859   $836.29   $836.30   $836.30