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 $81.56   13.527%   $92.5926   $92.59   $92.60   $92.60  
  Purchase #2 $52.78   6.717%   $56.3252   $56.33   $56.35   $56.30  
  Purchase #3 $169.87   6.248%   $180.4835   $180.48   $180.50   $180.50  
  Purchase #4 $21.56   7.624%   $23.2037   $23.20   $23.20   $23.20  
  Purchase #5 $160.60   7.689%   $172.9485   $172.95   $172.95   $172.90  
  Purchase #6 $91.30   4.418%   $95.3336   $95.33   $95.35   $95.30  
  Purchase #7 $68.38   10.435%   $75.5155   $75.52   $75.50   $75.50  
  7 purchase totals = $646.05       $696.4026   $696.40   $696.45   $696.30