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 $54.98   3.692%   $57.0099   $57.01   $57.00   $57.00  
  Purchase #2 $180.82   13.579%   $205.3735   $205.37   $205.35   $205.40  
  Purchase #3 $185.84   4.443%   $194.0969   $194.10   $194.10   $194.10  
  Purchase #4 $93.36   3.305%   $96.4455   $96.45   $96.45   $96.40  
  Purchase #5 $206.44   6.526%   $219.9123   $219.91   $219.90   $219.90  
  Purchase #6 $204.40   4.735%   $214.0783   $214.08   $214.10   $214.10  
  Purchase #7 $191.80   7.271%   $205.7458   $205.75   $205.75   $205.70  
  7 purchase totals = $1,117.64       $1,192.6622   $1,192.67   $1,192.65   $1,192.60