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 $245.49   11.184%   $272.9456   $272.95   $272.95   $272.90  
  Purchase #2 $146.69   6.826%   $156.7031   $156.70   $156.70   $156.70  
  Purchase #3 $124.39   11.595%   $138.813   $138.81   $138.80   $138.80  
  Purchase #4 $61.49   13.736%   $69.9363   $69.94   $69.95   $69.90  
  Purchase #5 $156.87   13.764%   $178.4616   $178.46   $178.45   $178.50  
  Purchase #6 $88.52   6.556%   $94.3234   $94.32   $94.30   $94.30  
  Purchase #7 $142.29   7.272%   $152.6373   $152.64   $152.65   $152.60  
  7 purchase totals = $965.74       $1,063.8203   $1,063.82   $1,063.80   $1,063.70