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 $44.83   13.182%   $50.7395   $50.74   $50.75   $50.70  
  Purchase #2 $23.98   4.458%   $25.049   $25.05   $25.05   $25.00  
  Purchase #3 $203.82   3.862%   $211.6915   $211.69   $211.70   $211.70  
  Purchase #4 $89.41   6.841%   $95.5265   $95.53   $95.55   $95.50  
  Purchase #5 $200.39   10.853%   $222.1383   $222.14   $222.15   $222.10  
  Purchase #6 $117.98   6.180%   $125.2712   $125.27   $125.25   $125.30  
  Purchase #7 $232.61   5.798%   $246.0967   $246.10   $246.10   $246.10  
  7 purchase totals = $913.02       $976.5127   $976.52   $976.55   $976.40