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 $95.95   11.726%   $107.2011   $107.20   $107.20   $107.20  
  Purchase #2 $210.76   10.373%   $232.6221   $232.62   $232.60   $232.60  
  Purchase #3 $108.25   10.839%   $119.9832   $119.98   $120.00   $120.00  
  Purchase #4 $179.52   7.764%   $193.4579   $193.46   $193.45   $193.50  
  Purchase #5 $57.60   4.722%   $60.3199   $60.32   $60.30   $60.30  
  Purchase #6 $117.25   3.621%   $121.4956   $121.50   $121.50   $121.50  
  Purchase #7 $233.78   4.313%   $243.8629   $243.86   $243.85   $243.90  
  7 purchase totals = $1,003.11       $1,078.9427   $1,078.94   $1,078.90   $1,079.00