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 $124.62   8.823%   $135.6152   $135.62   $135.60   $135.60  
  Purchase #2 $50.79   8.732%   $55.225   $55.23   $55.25   $55.20  
  Purchase #3 $150.76   9.565%   $165.1802   $165.18   $165.20   $165.20  
  Purchase #4 $113.27   9.699%   $124.2561   $124.26   $124.25   $124.30  
  Purchase #5 $5.62   7.543%   $6.0439   $6.04   $6.05   $6.00  
  Purchase #6 $152.54   11.263%   $169.7206   $169.72   $169.70   $169.70  
  Purchase #7 $199.52   13.752%   $226.958   $226.96   $226.95   $227.00  
  7 purchase totals = $797.12       $882.9990   $883.01   $883.00   $883.00