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 $178.67   12.661%   $201.2914   $201.29   $201.30   $201.30  
  Purchase #2 $159.35   8.325%   $172.6159   $172.62   $172.60   $172.60  
  Purchase #3 $219.52   10.509%   $242.5894   $242.59   $242.60   $242.60  
  Purchase #4 $240.30   11.656%   $268.3094   $268.31   $268.30   $268.30  
  Purchase #5 $67.42   4.780%   $70.6427   $70.64   $70.65   $70.60  
  Purchase #6 $151.29   12.462%   $170.1438   $170.14   $170.15   $170.10  
  Purchase #7 $178.88   10.524%   $197.7053   $197.71   $197.70   $197.70  
  7 purchase totals = $1,195.43       $1,323.2979   $1,323.30   $1,323.30   $1,323.20