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 $197.58   13.163%   $223.5875   $223.59   $223.60   $223.60  
  Purchase #2 $189.79   3.825%   $197.0495   $197.05   $197.05   $197.00  
  Purchase #3 $122.25   6.628%   $130.3527   $130.35   $130.35   $130.40  
  Purchase #4 $65.29   9.219%   $71.3091   $71.31   $71.30   $71.30  
  Purchase #5 $201.70   8.843%   $219.5363   $219.54   $219.55   $219.50  
  Purchase #6 $144.34   13.537%   $163.8793   $163.88   $163.90   $163.90  
  Purchase #7 $180.92   6.834%   $193.2841   $193.28   $193.30   $193.30  
  7 purchase totals = $1,101.87       $1,198.9985   $1,199.00   $1,199.05   $1,199.00