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 $88.47   5.515%   $93.3491   $93.35   $93.35   $93.30  
  Purchase #2 $87.39   10.813%   $96.8395   $96.84   $96.85   $96.80  
  Purchase #3 $158.61   6.748%   $169.313   $169.31   $169.30   $169.30  
  Purchase #4 $130.69   5.839%   $138.321   $138.32   $138.30   $138.30  
  Purchase #5 $149.60   11.351%   $166.5811   $166.58   $166.60   $166.60  
  Purchase #6 $102.79   6.381%   $109.349   $109.35   $109.35   $109.30  
  Purchase #7 $25.93   3.141%   $26.7445   $26.74   $26.75   $26.70  
  7 purchase totals = $743.48       $800.4972   $800.49   $800.50   $800.30