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 $76.65   12.309%   $86.0848   $86.08   $86.10   $86.10  
  Purchase #2 $225.42   12.445%   $253.4735   $253.47   $253.45   $253.50  
  Purchase #3 $197.62   11.731%   $220.8028   $220.80   $220.80   $220.80  
  Purchase #4 $53.79   6.728%   $57.409   $57.41   $57.40   $57.40  
  Purchase #5 $247.94   13.453%   $281.2954   $281.30   $281.30   $281.30  
  Purchase #6 $157.72   3.352%   $163.0068   $163.01   $163.00   $163.00  
  Purchase #7 $55.65   13.785%   $63.3214   $63.32   $63.30   $63.30  
  7 purchase totals = $1,014.79       $1,125.3937   $1,125.39   $1,125.35   $1,125.40