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 $245.74   7.471%   $264.0992   $264.10   $264.10   $264.10  
  Purchase #2 $194.86   8.613%   $211.6433   $211.64   $211.65   $211.60  
  Purchase #3 $60.36   5.558%   $63.7148   $63.71   $63.70   $63.70  
  Purchase #4 $175.72   8.505%   $190.665   $190.67   $190.65   $190.70  
  Purchase #5 $177.47   8.539%   $192.6242   $192.62   $192.60   $192.60  
  Purchase #6 $28.75   8.654%   $31.238   $31.24   $31.25   $31.20  
  Purchase #7 $191.58   10.410%   $211.5235   $211.52   $211.50   $211.50  
  7 purchase totals = $1,074.48       $1,165.5080   $1,165.50   $1,165.45   $1,165.40