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 $55.89   13.837%   $63.6235   $63.62   $63.60   $63.60  
  Purchase #2 $83.96   12.483%   $94.4407   $94.44   $94.45   $94.40  
  Purchase #3 $201.79   7.390%   $216.7023   $216.70   $216.70   $216.70  
  Purchase #4 $247.72   13.482%   $281.1176   $281.12   $281.10   $281.10  
  Purchase #5 $226.52   11.709%   $253.0432   $253.04   $253.05   $253.00  
  Purchase #6 $113.89   4.800%   $119.3567   $119.36   $119.35   $119.40  
  Purchase #7 $54.83   3.657%   $56.8351   $56.84   $56.85   $56.80  
  7 purchase totals = $984.60       $1,085.1191   $1,085.12   $1,085.10   $1,085.00