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 $220.51   3.766%   $228.8144   $228.81   $228.80   $228.80  
  Purchase #2 $214.51   5.394%   $226.0807   $226.08   $226.10   $226.10  
  Purchase #3 $131.73   12.747%   $148.5216   $148.52   $148.50   $148.50  
  Purchase #4 $60.72   9.249%   $66.336   $66.34   $66.35   $66.30  
  Purchase #5 $221.41   8.692%   $240.655   $240.66   $240.65   $240.70  
  Purchase #6 $58.80   5.797%   $62.2086   $62.21   $62.20   $62.20  
  Purchase #7 $38.67   8.470%   $41.9453   $41.95   $41.95   $41.90  
  7 purchase totals = $946.35       $1,014.5616   $1,014.57   $1,014.55   $1,014.50