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 $232.95   12.479%   $262.0198   $262.02   $262.00   $262.00  
  Purchase #2 $206.45   7.335%   $221.5931   $221.59   $221.60   $221.60  
  Purchase #3 $133.90   11.477%   $149.2677   $149.27   $149.25   $149.30  
  Purchase #4 $64.32   4.277%   $67.071   $67.07   $67.05   $67.10  
  Purchase #5 $66.52   5.340%   $70.0722   $70.07   $70.05   $70.10  
  Purchase #6 $198.81   6.296%   $211.3271   $211.33   $211.35   $211.30  
  Purchase #7 $189.59   7.832%   $204.4387   $204.44   $204.45   $204.40  
  7 purchase totals = $1,092.54       $1,185.7896   $1,185.79   $1,185.75   $1,185.80