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 $68.56   13.194%   $77.6058   $77.61   $77.60   $77.60  
  Purchase #2 $123.33   9.845%   $135.4718   $135.47   $135.45   $135.50  
  Purchase #3 $222.41   5.329%   $234.2622   $234.26   $234.25   $234.30  
  Purchase #4 $225.68   9.824%   $247.8508   $247.85   $247.85   $247.90  
  Purchase #5 $16.44   3.254%   $16.975   $16.98   $17.00   $17.00  
  Purchase #6 $212.56   13.148%   $240.5074   $240.51   $240.50   $240.50  
  Purchase #7 $148.59   13.157%   $168.14   $168.14   $168.15   $168.10  
  7 purchase totals = $1,017.57       $1,120.8130   $1,120.82   $1,120.80   $1,120.90