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 $167.88   9.408%   $183.6742   $183.67   $183.65   $183.70  
  Purchase #2 $189.75   3.210%   $195.841   $195.84   $195.85   $195.80  
  Purchase #3 $155.58   3.451%   $160.9491   $160.95   $160.95   $160.90  
  Purchase #4 $236.27   8.348%   $255.9938   $255.99   $256.00   $256.00  
  Purchase #5 $56.94   6.365%   $60.5642   $60.56   $60.55   $60.60  
  Purchase #6 $120.43   6.613%   $128.394   $128.39   $128.40   $128.40  
  Purchase #7 $36.60   5.373%   $38.5665   $38.57   $38.55   $38.60  
  7 purchase totals = $963.45       $1,023.9828   $1,023.97   $1,023.95   $1,024.00