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 $27.46   9.499%   $30.0684   $30.07   $30.05   $30.10  
  Purchase #2 $94.52   12.463%   $106.3   $106.30   $106.30   $106.30  
  Purchase #3 $184.56   11.467%   $205.7235   $205.72   $205.70   $205.70  
  Purchase #4 $138.58   6.638%   $147.7789   $147.78   $147.80   $147.80  
  Purchase #5 $28.62   13.720%   $32.5467   $32.55   $32.55   $32.50  
  Purchase #6 $88.35   3.177%   $91.1569   $91.16   $91.15   $91.20  
  Purchase #7 $184.26   6.652%   $196.517   $196.52   $196.50   $196.50  
  7 purchase totals = $746.35       $810.0914   $810.10   $810.05   $810.10