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 $157.37   11.170%   $174.9482   $174.95   $174.95   $174.90  
  Purchase #2 $85.53   7.200%   $91.6882   $91.69   $91.70   $91.70  
  Purchase #3 $206.52   13.244%   $233.8715   $233.87   $233.85   $233.90  
  Purchase #4 $231.59   13.259%   $262.2965   $262.30   $262.30   $262.30  
  Purchase #5 $12.26   12.789%   $13.8279   $13.83   $13.85   $13.80  
  Purchase #6 $59.35   10.153%   $65.3758   $65.38   $65.40   $65.40  
  Purchase #7 $201.67   9.703%   $221.238   $221.24   $221.25   $221.20  
  7 purchase totals = $954.29       $1,063.2461   $1,063.26   $1,063.30   $1,063.20