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 $61.26   4.847%   $64.2293   $64.23   $64.25   $64.20  
  Purchase #2 $17.52   7.270%   $18.7937   $18.79   $18.80   $18.80  
  Purchase #3 $90.37   6.371%   $96.1275   $96.13   $96.15   $96.10  
  Purchase #4 $139.31   6.311%   $148.1019   $148.10   $148.10   $148.10  
  Purchase #5 $205.85   12.848%   $232.2976   $232.30   $232.30   $232.30  
  Purchase #6 $8.99   3.782%   $9.33   $9.33   $9.35   $9.30  
  Purchase #7 $28.58   7.764%   $30.799   $30.80   $30.80   $30.80  
  7 purchase totals = $551.88       $599.6790   $599.68   $599.75   $599.60