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 $112.86   10.627%   $124.8536   $124.85   $124.85   $124.90  
  Purchase #2 $43.38   12.582%   $48.8381   $48.84   $48.85   $48.80  
  Purchase #3 $115.72   4.200%   $120.5802   $120.58   $120.60   $120.60  
  Purchase #4 $237.81   10.450%   $262.6611   $262.66   $262.65   $262.70  
  Purchase #5 $95.55   3.523%   $98.9162   $98.92   $98.90   $98.90  
  Purchase #6 $209.82   12.272%   $235.5691   $235.57   $235.55   $235.60  
  Purchase #7 $44.73   4.647%   $46.8086   $46.81   $46.80   $46.80  
  7 purchase totals = $859.87       $938.2269   $938.23   $938.20   $938.30