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 $33.88   6.279%   $36.0073   $36.01   $36.00   $36.00  
  Purchase #2 $226.30   5.814%   $239.4571   $239.46   $239.45   $239.50  
  Purchase #3 $107.61   8.455%   $116.7084   $116.71   $116.70   $116.70  
  Purchase #4 $167.58   4.567%   $175.2334   $175.23   $175.25   $175.20  
  Purchase #5 $108.80   13.590%   $123.5859   $123.59   $123.60   $123.60  
  Purchase #6 $192.84   4.459%   $201.4387   $201.44   $201.45   $201.40  
  Purchase #7 $247.55   5.118%   $260.2196   $260.22   $260.20   $260.20  
  7 purchase totals = $1,084.56       $1,152.6504   $1,152.66   $1,152.65   $1,152.60