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 $72.82   5.343%   $76.7108   $76.71   $76.70   $76.70  
  Purchase #2 $58.98   4.304%   $61.5185   $61.52   $61.50   $61.50  
  Purchase #3 $240.67   6.373%   $256.0079   $256.01   $256.00   $256.00  
  Purchase #4 $185.28   12.118%   $207.7322   $207.73   $207.75   $207.70  
  Purchase #5 $97.80   5.516%   $103.1946   $103.19   $103.20   $103.20  
  Purchase #6 $223.86   5.488%   $236.1454   $236.15   $236.15   $236.10  
  Purchase #7 $204.48   6.740%   $218.262   $218.26   $218.25   $218.30  
  7 purchase totals = $1,083.89       $1,159.5714   $1,159.57   $1,159.55   $1,159.50