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 $164.82   6.808%   $176.0409   $176.04   $176.05   $176.00  
  Purchase #2 $9.76   12.415%   $10.9717   $10.97   $10.95   $11.00  
  Purchase #3 $59.58   7.667%   $64.148   $64.15   $64.15   $64.10  
  Purchase #4 $232.80   13.355%   $263.8904   $263.89   $263.90   $263.90  
  Purchase #5 $58.65   6.206%   $62.2898   $62.29   $62.30   $62.30  
  Purchase #6 $85.90   9.605%   $94.1507   $94.15   $94.15   $94.20  
  Purchase #7 $147.36   11.860%   $164.8369   $164.84   $164.85   $164.80  
  7 purchase totals = $758.87       $836.3284   $836.33   $836.35   $836.30