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 $168.94   9.237%   $184.545   $184.55   $184.55   $184.50  
  Purchase #2 $73.78   6.550%   $78.6126   $78.61   $78.60   $78.60  
  Purchase #3 $95.83   13.366%   $108.6386   $108.64   $108.65   $108.60  
  Purchase #4 $147.26   4.606%   $154.0428   $154.04   $154.05   $154.00  
  Purchase #5 $156.33   13.226%   $177.0062   $177.01   $177.00   $177.00  
  Purchase #6 $58.28   9.243%   $63.6668   $63.67   $63.65   $63.70  
  Purchase #7 $226.34   11.647%   $252.7018   $252.70   $252.70   $252.70  
  7 purchase totals = $926.76       $1,019.2138   $1,019.22   $1,019.20   $1,019.10