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 $87.97   6.310%   $93.5209   $93.52   $93.50   $93.50  
  Purchase #2 $224.55   3.549%   $232.5193   $232.52   $232.50   $232.50  
  Purchase #3 $142.60   9.162%   $155.665   $155.67   $155.65   $155.70  
  Purchase #4 $57.32   11.277%   $63.784   $63.78   $63.80   $63.80  
  Purchase #5 $171.90   5.719%   $181.731   $181.73   $181.75   $181.70  
  Purchase #6 $240.25   3.539%   $248.7524   $248.75   $248.75   $248.80  
  Purchase #7 $228.68   3.695%   $237.1297   $237.13   $237.15   $237.10  
  7 purchase totals = $1,153.27       $1,213.1023   $1,213.10   $1,213.10   $1,213.10