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 $54.33   8.635%   $59.0214   $59.02   $59.00   $59.00  
  Purchase #2 $144.58   7.633%   $155.6158   $155.62   $155.60   $155.60  
  Purchase #3 $89.65   7.198%   $96.103   $96.10   $96.10   $96.10  
  Purchase #4 $201.26   11.722%   $224.8517   $224.85   $224.85   $224.90  
  Purchase #5 $147.45   5.856%   $156.0847   $156.08   $156.10   $156.10  
  Purchase #6 $23.70   3.273%   $24.4757   $24.48   $24.50   $24.50  
  Purchase #7 $231.37   8.277%   $250.5205   $250.52   $250.50   $250.50  
  7 purchase totals = $892.34       $966.6728   $966.67   $966.65   $966.70