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 $97.49   9.594%   $106.8432   $106.84   $106.85   $106.80  
  Purchase #2 $150.79   10.647%   $166.8446   $166.84   $166.85   $166.80  
  Purchase #3 $63.83   6.185%   $67.7779   $67.78   $67.80   $67.80  
  Purchase #4 $234.48   9.210%   $256.0756   $256.08   $256.10   $256.10  
  Purchase #5 $54.82   12.609%   $61.7323   $61.73   $61.75   $61.70  
  Purchase #6 $203.41   8.320%   $220.3337   $220.33   $220.35   $220.30  
  Purchase #7 $137.32   8.197%   $148.5761   $148.58   $148.60   $148.60  
  7 purchase totals = $942.14       $1,028.1834   $1,028.18   $1,028.30   $1,028.10