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 $195.97   11.141%   $217.803   $217.80   $217.80   $217.80  
  Purchase #2 $217.28   13.382%   $246.3564   $246.36   $246.35   $246.40  
  Purchase #3 $159.92   4.690%   $167.4202   $167.42   $167.40   $167.40  
  Purchase #4 $216.36   5.588%   $228.4502   $228.45   $228.45   $228.50  
  Purchase #5 $48.90   6.359%   $52.0096   $52.01   $52.00   $52.00  
  Purchase #6 $20.55   13.762%   $23.3781   $23.38   $23.40   $23.40  
  Purchase #7 $90.30   9.258%   $98.66   $98.66   $98.65   $98.70  
  7 purchase totals = $949.28       $1,034.0775   $1,034.08   $1,034.05   $1,034.20