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 $41.28   4.851%   $43.2825   $43.28   $43.30   $43.30  
  Purchase #2 $69.54   6.862%   $74.3118   $74.31   $74.30   $74.30  
  Purchase #3 $235.38   9.210%   $257.0585   $257.06   $257.05   $257.10  
  Purchase #4 $84.86   9.188%   $92.6569   $92.66   $92.65   $92.70  
  Purchase #5 $198.82   13.833%   $226.3228   $226.32   $226.30   $226.30  
  Purchase #6 $102.52   5.471%   $108.1289   $108.13   $108.15   $108.10  
  Purchase #7 $154.25   12.538%   $173.5899   $173.59   $173.60   $173.60  
  7 purchase totals = $886.65       $975.3513   $975.35   $975.35   $975.40