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 $52.33   12.109%   $58.6666   $58.67   $58.65   $58.70  
  Purchase #2 $103.52   9.583%   $113.4403   $113.44   $113.45   $113.40  
  Purchase #3 $174.98   5.564%   $184.7159   $184.72   $184.70   $184.70  
  Purchase #4 $24.64   6.535%   $26.2502   $26.25   $26.25   $26.30  
  Purchase #5 $204.64   10.157%   $225.4253   $225.43   $225.45   $225.40  
  Purchase #6 $195.35   13.853%   $222.4118   $222.41   $222.40   $222.40  
  Purchase #7 $180.93   3.741%   $187.6986   $187.70   $187.70   $187.70  
  7 purchase totals = $936.39       $1,018.6087   $1,018.62   $1,018.60   $1,018.60