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 $79.75   8.426%   $86.4697   $86.47   $86.45   $86.50  
  Purchase #2 $222.58   10.156%   $245.1852   $245.19   $245.20   $245.20  
  Purchase #3 $10.90   8.147%   $11.788   $11.79   $11.80   $11.80  
  Purchase #4 $82.35   8.632%   $89.4585   $89.46   $89.45   $89.50  
  Purchase #5 $77.27   4.192%   $80.5092   $80.51   $80.50   $80.50  
  Purchase #6 $5.52   11.128%   $6.1343   $6.13   $6.15   $6.10  
  Purchase #7 $147.32   7.281%   $158.0464   $158.05   $158.05   $158.00  
  7 purchase totals = $625.69       $677.5913   $677.60   $677.60   $677.60