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 $92.37   9.162%   $100.8329   $100.83   $100.85   $100.80  
  Purchase #2 $47.87   5.357%   $50.4344   $50.43   $50.45   $50.40  
  Purchase #3 $106.69   13.708%   $121.3151   $121.32   $121.30   $121.30  
  Purchase #4 $121.97   7.699%   $131.3605   $131.36   $131.35   $131.40  
  Purchase #5 $177.54   4.585%   $185.6802   $185.68   $185.70   $185.70  
  Purchase #6 $102.43   7.174%   $109.7783   $109.78   $109.80   $109.80  
  Purchase #7 $184.46   9.338%   $201.6849   $201.68   $201.70   $201.70  
  7 purchase totals = $833.33       $901.0863   $901.08   $901.15   $901.10