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 $164.86   11.205%   $183.3326   $183.33   $183.35   $183.30  
  Purchase #2 $187.77   8.465%   $203.6647   $203.66   $203.65   $203.70  
  Purchase #3 $87.31   8.857%   $95.043   $95.04   $95.05   $95.00  
  Purchase #4 $44.34   4.210%   $46.2067   $46.21   $46.20   $46.20  
  Purchase #5 $14.58   12.685%   $16.4295   $16.43   $16.45   $16.40  
  Purchase #6 $45.37   6.850%   $48.4778   $48.48   $48.50   $48.50  
  Purchase #7 $214.53   6.132%   $227.685   $227.69   $227.70   $227.70  
  7 purchase totals = $758.76       $820.8393   $820.84   $820.90   $820.80