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 $188.87   10.702%   $209.0829   $209.08   $209.10   $209.10  
  Purchase #2 $127.95   7.816%   $137.9506   $137.95   $137.95   $138.00  
  Purchase #3 $13.79   10.692%   $15.2644   $15.26   $15.25   $15.30  
  Purchase #4 $183.97   11.594%   $205.2995   $205.30   $205.30   $205.30  
  Purchase #5 $244.51   12.651%   $275.443   $275.44   $275.45   $275.40  
  Purchase #6 $101.28   4.807%   $106.1485   $106.15   $106.15   $106.10  
  Purchase #7 $111.46   8.327%   $120.7413   $120.74   $120.75   $120.70  
  7 purchase totals = $971.83       $1,069.9302   $1,069.92   $1,069.95   $1,069.90