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 $161.28   5.665%   $170.4165   $170.42   $170.40   $170.40  
  Purchase #2 $9.86   9.471%   $10.7938   $10.79   $10.80   $10.80  
  Purchase #3 $170.51   4.107%   $177.5128   $177.51   $177.50   $177.50  
  Purchase #4 $136.68   8.158%   $147.8304   $147.83   $147.85   $147.80  
  Purchase #5 $165.88   5.389%   $174.8193   $174.82   $174.80   $174.80  
  Purchase #6 $59.45   5.854%   $62.9302   $62.93   $62.95   $62.90  
  Purchase #7 $43.78   7.335%   $46.9913   $46.99   $47.00   $47.00  
  7 purchase totals = $747.44       $791.2943   $791.29   $791.30   $791.20