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 $82.49   13.445%   $93.5808   $93.58   $93.60   $93.60  
  Purchase #2 $192.72   13.622%   $218.9723   $218.97   $218.95   $219.00  
  Purchase #3 $18.96   12.596%   $21.3482   $21.35   $21.35   $21.30  
  Purchase #4 $109.67   9.560%   $120.1545   $120.15   $120.15   $120.20  
  Purchase #5 $231.36   11.784%   $258.6235   $258.62   $258.60   $258.60  
  Purchase #6 $211.50   11.212%   $235.2134   $235.21   $235.20   $235.20  
  Purchase #7 $88.37   9.741%   $96.9781   $96.98   $97.00   $97.00  
  7 purchase totals = $935.07       $1,044.8708   $1,044.86   $1,044.85   $1,044.90