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 $183.84   13.865%   $209.3294   $209.33   $209.35   $209.30  
  Purchase #2 $64.52   5.352%   $67.9731   $67.97   $67.95   $68.00  
  Purchase #3 $59.83   3.520%   $61.936   $61.94   $61.95   $61.90  
  Purchase #4 $246.32   3.316%   $254.488   $254.49   $254.50   $254.50  
  Purchase #5 $181.82   11.338%   $202.4348   $202.43   $202.45   $202.40  
  Purchase #6 $238.42   7.656%   $256.6734   $256.67   $256.65   $256.70  
  Purchase #7 $112.34   11.783%   $125.577   $125.58   $125.60   $125.60  
  7 purchase totals = $1,087.09       $1,178.4117   $1,178.41   $1,178.45   $1,178.40