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 $186.38   8.180%   $201.6259   $201.63   $201.65   $201.60  
  Purchase #2 $230.32   9.618%   $252.4722   $252.47   $252.45   $252.50  
  Purchase #3 $120.53   6.540%   $128.4127   $128.41   $128.40   $128.40  
  Purchase #4 $118.95   4.282%   $124.0434   $124.04   $124.05   $124.00  
  Purchase #5 $101.50   6.167%   $107.7595   $107.76   $107.75   $107.80  
  Purchase #6 $113.86   6.561%   $121.3304   $121.33   $121.35   $121.30  
  Purchase #7 $54.68   9.116%   $59.6646   $59.66   $59.65   $59.70  
  7 purchase totals = $926.22       $995.3087   $995.30   $995.30   $995.30