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 $180.59   11.640%   $201.6107   $201.61   $201.60   $201.60  
  Purchase #2 $103.25   6.815%   $110.2865   $110.29   $110.30   $110.30  
  Purchase #3 $238.62   11.645%   $266.4073   $266.41   $266.40   $266.40  
  Purchase #4 $34.75   6.135%   $36.8819   $36.88   $36.90   $36.90  
  Purchase #5 $239.43   6.419%   $254.799   $254.80   $254.80   $254.80  
  Purchase #6 $51.97   13.542%   $59.0078   $59.01   $59.00   $59.00  
  Purchase #7 $95.67   12.516%   $107.6441   $107.64   $107.65   $107.60  
  7 purchase totals = $944.28       $1,036.6373   $1,036.64   $1,036.65   $1,036.60