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 $153.93   7.368%   $165.2716   $165.27   $165.25   $165.30  
  Purchase #2 $206.74   11.707%   $230.9431   $230.94   $230.95   $230.90  
  Purchase #3 $98.31   9.124%   $107.2798   $107.28   $107.30   $107.30  
  Purchase #4 $156.35   10.241%   $172.3618   $172.36   $172.35   $172.40  
  Purchase #5 $171.45   12.874%   $193.5225   $193.52   $193.50   $193.50  
  Purchase #6 $48.32   4.294%   $50.3949   $50.39   $50.40   $50.40  
  Purchase #7 $137.88   8.426%   $149.4978   $149.50   $149.50   $149.50  
  7 purchase totals = $972.98       $1,069.2715   $1,069.26   $1,069.25   $1,069.30