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 $173.92   13.681%   $197.714   $197.71   $197.70   $197.70  
  Purchase #2 $24.89   8.689%   $27.0527   $27.05   $27.05   $27.10  
  Purchase #3 $106.37   12.780%   $119.9641   $119.96   $119.95   $120.00  
  Purchase #4 $70.52   13.363%   $79.9436   $79.94   $79.95   $79.90  
  Purchase #5 $124.68   5.806%   $131.9189   $131.92   $131.90   $131.90  
  Purchase #6 $245.79   5.470%   $259.2347   $259.23   $259.25   $259.20  
  Purchase #7 $187.58   9.643%   $205.6683   $205.67   $205.65   $205.70  
  7 purchase totals = $933.75       $1,021.4963   $1,021.48   $1,021.45   $1,021.50