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 $179.47   13.383%   $203.4885   $203.49   $203.50   $203.50  
  Purchase #2 $100.27   3.392%   $103.6712   $103.67   $103.65   $103.70  
  Purchase #3 $122.25   11.485%   $136.2904   $136.29   $136.30   $136.30  
  Purchase #4 $244.64   11.834%   $273.5907   $273.59   $273.60   $273.60  
  Purchase #5 $172.59   9.716%   $189.3588   $189.36   $189.35   $189.40  
  Purchase #6 $183.26   12.147%   $205.5206   $205.52   $205.50   $205.50  
  Purchase #7 $51.34   4.596%   $53.6996   $53.70   $53.70   $53.70  
  7 purchase totals = $1,053.82       $1,165.6198   $1,165.62   $1,165.60   $1,165.70