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 $48.91   7.502%   $52.5792   $52.58   $52.60   $52.60  
  Purchase #2 $204.68   10.256%   $225.672   $225.67   $225.65   $225.70  
  Purchase #3 $50.85   4.126%   $52.9481   $52.95   $52.95   $52.90  
  Purchase #4 $246.96   11.403%   $275.1208   $275.12   $275.10   $275.10  
  Purchase #5 $165.42   7.170%   $177.2806   $177.28   $177.30   $177.30  
  Purchase #6 $199.62   10.655%   $220.8895   $220.89   $220.90   $220.90  
  Purchase #7 $220.81   7.247%   $236.8121   $236.81   $236.80   $236.80  
  7 purchase totals = $1,137.25       $1,241.3023   $1,241.30   $1,241.30   $1,241.30