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 $52.96   11.695%   $59.1537   $59.15   $59.15   $59.20  
  Purchase #2 $120.97   11.635%   $135.0449   $135.04   $135.05   $135.00  
  Purchase #3 $78.86   8.492%   $85.5568   $85.56   $85.55   $85.60  
  Purchase #4 $115.64   4.779%   $121.1664   $121.17   $121.15   $121.20  
  Purchase #5 $115.65   8.829%   $125.8607   $125.86   $125.85   $125.90  
  Purchase #6 $245.60   5.324%   $258.6757   $258.68   $258.70   $258.70  
  Purchase #7 $213.58   12.735%   $240.7794   $240.78   $240.80   $240.80  
  7 purchase totals = $943.26       $1,026.2376   $1,026.24   $1,026.25   $1,026.40