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 $156.77   11.230%   $174.3753   $174.38   $174.40   $174.40  
  Purchase #2 $169.35   9.103%   $184.7659   $184.77   $184.75   $184.80  
  Purchase #3 $186.87   4.702%   $195.6566   $195.66   $195.65   $195.70  
  Purchase #4 $115.49   9.229%   $126.1486   $126.15   $126.15   $126.10  
  Purchase #5 $170.99   3.107%   $176.3027   $176.30   $176.30   $176.30  
  Purchase #6 $54.25   10.612%   $60.007   $60.01   $60.00   $60.00  
  Purchase #7 $118.25   5.716%   $125.0092   $125.01   $125.00   $125.00  
  7 purchase totals = $971.97       $1,042.2653   $1,042.28   $1,042.25   $1,042.30