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 $137.77   9.774%   $151.2356   $151.24   $151.25   $151.20  
  Purchase #2 $184.94   3.253%   $190.9561   $190.96   $190.95   $191.00  
  Purchase #3 $169.40   4.108%   $176.359   $176.36   $176.35   $176.40  
  Purchase #4 $180.58   11.309%   $201.0018   $201.00   $201.00   $201.00  
  Purchase #5 $126.26   6.194%   $134.0805   $134.08   $134.10   $134.10  
  Purchase #6 $219.39   11.617%   $244.8765   $244.88   $244.90   $244.90  
  Purchase #7 $35.44   3.598%   $36.7151   $36.72   $36.70   $36.70  
  7 purchase totals = $1,053.78       $1,135.2246   $1,135.24   $1,135.25   $1,135.30