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 $228.82   3.551%   $236.9454   $236.95   $236.95   $236.90  
  Purchase #2 $139.39   12.252%   $156.4681   $156.47   $156.45   $156.50  
  Purchase #3 $142.92   3.142%   $147.4105   $147.41   $147.40   $147.40  
  Purchase #4 $220.26   10.106%   $242.5195   $242.52   $242.50   $242.50  
  Purchase #5 $22.72   13.869%   $25.871   $25.87   $25.85   $25.90  
  Purchase #6 $71.98   8.279%   $77.9392   $77.94   $77.95   $77.90  
  Purchase #7 $161.26   7.107%   $172.7207   $172.72   $172.70   $172.70  
  7 purchase totals = $987.35       $1,059.8744   $1,059.88   $1,059.80   $1,059.80