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 $167.84   9.523%   $183.8234   $183.82   $183.80   $183.80  
  Purchase #2 $183.52   8.394%   $198.9247   $198.92   $198.90   $198.90  
  Purchase #3 $138.66   8.556%   $150.5237   $150.52   $150.50   $150.50  
  Purchase #4 $22.53   7.670%   $24.2581   $24.26   $24.25   $24.30  
  Purchase #5 $206.84   11.323%   $230.2605   $230.26   $230.25   $230.30  
  Purchase #6 $248.46   4.853%   $260.5178   $260.52   $260.50   $260.50  
  Purchase #7 $73.31   7.406%   $78.7393   $78.74   $78.75   $78.70  
  7 purchase totals = $1,041.16       $1,127.0475   $1,127.04   $1,126.95   $1,127.00