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 $70.81   9.514%   $77.5469   $77.55   $77.55   $77.50  
  Purchase #2 $159.65   13.602%   $181.3656   $181.37   $181.35   $181.40  
  Purchase #3 $99.64   4.279%   $103.9036   $103.90   $103.90   $103.90  
  Purchase #4 $213.94   11.174%   $237.8457   $237.85   $237.85   $237.80  
  Purchase #5 $203.29   10.503%   $224.6415   $224.64   $224.65   $224.60  
  Purchase #6 $49.44   11.750%   $55.2492   $55.25   $55.25   $55.20  
  Purchase #7 $149.34   13.367%   $169.3023   $169.30   $169.30   $169.30  
  7 purchase totals = $946.11       $1,049.8548   $1,049.86   $1,049.85   $1,049.70