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 $162.43   11.276%   $180.7456   $180.75   $180.75   $180.70  
  Purchase #2 $231.97   6.247%   $246.4612   $246.46   $246.45   $246.50  
  Purchase #3 $134.72   8.715%   $146.4608   $146.46   $146.45   $146.50  
  Purchase #4 $232.94   6.526%   $248.1417   $248.14   $248.15   $248.10  
  Purchase #5 $65.91   12.614%   $74.2239   $74.22   $74.20   $74.20  
  Purchase #6 $224.58   11.672%   $250.793   $250.79   $250.80   $250.80  
  Purchase #7 $217.52   6.760%   $232.2244   $232.22   $232.20   $232.20  
  7 purchase totals = $1,270.07       $1,379.0506   $1,379.04   $1,379.00   $1,379.00