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 $194.83   13.277%   $220.6976   $220.70   $220.70   $220.70  
  Purchase #2 $172.32   6.807%   $184.0498   $184.05   $184.05   $184.00  
  Purchase #3 $145.35   13.514%   $164.9926   $164.99   $165.00   $165.00  
  Purchase #4 $24.79   6.395%   $26.3753   $26.38   $26.40   $26.40  
  Purchase #5 $204.60   8.862%   $222.7317   $222.73   $222.75   $222.70  
  Purchase #6 $45.74   13.297%   $51.822   $51.82   $51.80   $51.80  
  Purchase #7 $220.59   5.573%   $232.8835   $232.88   $232.90   $232.90  
  7 purchase totals = $1,008.22       $1,103.5525   $1,103.55   $1,103.60   $1,103.50