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 $77.52   10.713%   $85.8247   $85.82   $85.80   $85.80  
  Purchase #2 $122.28   13.494%   $138.7805   $138.78   $138.80   $138.80  
  Purchase #3 $135.82   7.268%   $145.6914   $145.69   $145.70   $145.70  
  Purchase #4 $249.40   11.840%   $278.929   $278.93   $278.95   $278.90  
  Purchase #5 $141.72   11.697%   $158.297   $158.30   $158.30   $158.30  
  Purchase #6 $67.44   9.232%   $73.6661   $73.67   $73.65   $73.70  
  Purchase #7 $124.69   9.201%   $136.1627   $136.16   $136.15   $136.20  
  7 purchase totals = $918.87       $1,017.3514   $1,017.35   $1,017.35   $1,017.40