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 $51.74   11.395%   $57.6358   $57.64   $57.65   $57.60  
  Purchase #2 $32.93   4.504%   $34.4132   $34.41   $34.40   $34.40  
  Purchase #3 $220.39   10.153%   $242.7662   $242.77   $242.75   $242.80  
  Purchase #4 $167.60   7.502%   $180.1734   $180.17   $180.15   $180.20  
  Purchase #5 $58.84   10.494%   $65.0147   $65.01   $65.00   $65.00  
  Purchase #6 $120.90   7.682%   $130.1875   $130.19   $130.20   $130.20  
  Purchase #7 $131.84   7.701%   $141.993   $141.99   $142.00   $142.00  
  7 purchase totals = $784.24       $852.1838   $852.18   $852.15   $852.20