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 $173.94   12.116%   $195.0146   $195.01   $195.00   $195.00  
  Purchase #2 $57.26   3.820%   $59.4473   $59.45   $59.45   $59.40  
  Purchase #3 $35.68   8.737%   $38.7974   $38.80   $38.80   $38.80  
  Purchase #4 $33.34   9.727%   $36.583   $36.58   $36.60   $36.60  
  Purchase #5 $167.84   3.838%   $174.2817   $174.28   $174.30   $174.30  
  Purchase #6 $116.28   11.850%   $130.0592   $130.06   $130.05   $130.10  
  Purchase #7 $156.26   9.551%   $171.1844   $171.18   $171.20   $171.20  
  7 purchase totals = $740.60       $805.3676   $805.36   $805.40   $805.40