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 $33.95   10.850%   $37.6336   $37.63   $37.65   $37.60  
  Purchase #2 $119.29   12.273%   $133.9305   $133.93   $133.95   $133.90  
  Purchase #3 $235.69   8.253%   $255.1415   $255.14   $255.15   $255.10  
  Purchase #4 $223.52   10.420%   $246.8108   $246.81   $246.80   $246.80  
  Purchase #5 $121.70   12.323%   $136.6971   $136.70   $136.70   $136.70  
  Purchase #6 $166.57   4.613%   $174.2539   $174.25   $174.25   $174.30  
  Purchase #7 $77.31   11.124%   $85.91   $85.91   $85.90   $85.90  
  7 purchase totals = $978.03       $1,070.3774   $1,070.37   $1,070.40   $1,070.30