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 $196.29   4.582%   $205.284   $205.28   $205.30   $205.30  
  Purchase #2 $18.48   8.713%   $20.0902   $20.09   $20.10   $20.10  
  Purchase #3 $57.98   4.657%   $60.6801   $60.68   $60.70   $60.70  
  Purchase #4 $100.74   8.394%   $109.1961   $109.20   $109.20   $109.20  
  Purchase #5 $114.76   11.637%   $128.1146   $128.11   $128.10   $128.10  
  Purchase #6 $158.90   4.445%   $165.9631   $165.96   $165.95   $166.00  
  Purchase #7 $88.58   6.169%   $94.0445   $94.04   $94.05   $94.00  
  7 purchase totals = $735.73       $783.3726   $783.36   $783.40   $783.40