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 $183.26   11.128%   $203.6532   $203.65   $203.65   $203.70  
  Purchase #2 $83.68   12.658%   $94.2722   $94.27   $94.25   $94.30  
  Purchase #3 $80.27   13.572%   $91.1642   $91.16   $91.15   $91.20  
  Purchase #4 $154.35   7.299%   $165.616   $165.62   $165.60   $165.60  
  Purchase #5 $210.51   11.146%   $233.9734   $233.97   $233.95   $234.00  
  Purchase #6 $160.52   13.408%   $182.0425   $182.04   $182.05   $182.00  
  Purchase #7 $181.48   8.722%   $197.3087   $197.31   $197.30   $197.30  
  7 purchase totals = $1,054.07       $1,168.0302   $1,168.02   $1,167.95   $1,168.10