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 $181.84   10.640%   $201.1878   $201.19   $201.20   $201.20  
  Purchase #2 $168.77   11.386%   $187.9862   $187.99   $188.00   $188.00  
  Purchase #3 $163.72   12.613%   $184.37   $184.37   $184.35   $184.40  
  Purchase #4 $24.51   8.515%   $26.597   $26.60   $26.60   $26.60  
  Purchase #5 $101.69   8.133%   $109.9604   $109.96   $109.95   $110.00  
  Purchase #6 $167.61   9.160%   $182.9631   $182.96   $182.95   $183.00  
  Purchase #7 $137.74   7.440%   $147.9879   $147.99   $148.00   $148.00  
  7 purchase totals = $945.88       $1,041.0524   $1,041.06   $1,041.05   $1,041.20