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 $61.59   5.834%   $65.1832   $65.18   $65.20   $65.20  
  Purchase #2 $41.94   3.142%   $43.2578   $43.26   $43.25   $43.30  
  Purchase #3 $167.82   3.483%   $173.6652   $173.67   $173.65   $173.70  
  Purchase #4 $226.45   4.636%   $236.9482   $236.95   $236.95   $236.90  
  Purchase #5 $212.93   12.688%   $239.9466   $239.95   $239.95   $239.90  
  Purchase #6 $61.41   5.507%   $64.7918   $64.79   $64.80   $64.80  
  Purchase #7 $167.89   11.556%   $187.2914   $187.29   $187.30   $187.30  
  7 purchase totals = $940.03       $1,011.0842   $1,011.09   $1,011.10   $1,011.10