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 $148.89   13.642%   $169.2016   $169.20   $169.20   $169.20  
  Purchase #2 $211.25   10.410%   $233.2411   $233.24   $233.25   $233.20  
  Purchase #3 $175.40   6.169%   $186.2204   $186.22   $186.20   $186.20  
  Purchase #4 $240.83   7.475%   $258.832   $258.83   $258.85   $258.80  
  Purchase #5 $165.59   7.805%   $178.5143   $178.51   $178.50   $178.50  
  Purchase #6 $181.75   11.130%   $201.9788   $201.98   $202.00   $202.00  
  Purchase #7 $94.88   12.280%   $106.5313   $106.53   $106.55   $106.50  
  7 purchase totals = $1,218.59       $1,334.5195   $1,334.51   $1,334.55   $1,334.40