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 $243.38   10.462%   $268.8424   $268.84   $268.85   $268.80  
  Purchase #2 $105.69   4.463%   $110.4069   $110.41   $110.40   $110.40  
  Purchase #3 $177.43   3.741%   $184.0677   $184.07   $184.05   $184.10  
  Purchase #4 $150.65   8.664%   $163.7023   $163.70   $163.70   $163.70  
  Purchase #5 $79.92   7.424%   $85.8533   $85.85   $85.85   $85.90  
  Purchase #6 $123.80   7.297%   $132.8337   $132.83   $132.85   $132.80  
  Purchase #7 $104.69   6.527%   $111.5231   $111.52   $111.50   $111.50  
  7 purchase totals = $985.56       $1,057.2294   $1,057.22   $1,057.20   $1,057.20