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 $183.48   10.409%   $202.5784   $202.58   $202.60   $202.60  
  Purchase #2 $25.34   3.446%   $26.2132   $26.21   $26.20   $26.20  
  Purchase #3 $195.43   10.307%   $215.573   $215.57   $215.55   $215.60  
  Purchase #4 $48.57   12.286%   $54.5373   $54.54   $54.55   $54.50  
  Purchase #5 $95.95   3.797%   $99.5932   $99.59   $99.60   $99.60  
  Purchase #6 $127.87   4.166%   $133.1971   $133.20   $133.20   $133.20  
  Purchase #7 $198.29   13.656%   $225.3685   $225.37   $225.35   $225.40  
  7 purchase totals = $874.93       $957.0607   $957.06   $957.05   $957.10