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 $238.58   5.751%   $252.3007   $252.30   $252.30   $252.30  
  Purchase #2 $116.96   4.212%   $121.8864   $121.89   $121.90   $121.90  
  Purchase #3 $189.95   4.536%   $198.5661   $198.57   $198.55   $198.60  
  Purchase #4 $225.78   5.764%   $238.794   $238.79   $238.80   $238.80  
  Purchase #5 $115.78   12.285%   $130.0036   $130.00   $130.00   $130.00  
  Purchase #6 $228.68   11.854%   $255.7877   $255.79   $255.80   $255.80  
  Purchase #7 $65.49   3.748%   $67.9446   $67.94   $67.95   $67.90  
  7 purchase totals = $1,181.22       $1,265.2831   $1,265.28   $1,265.30   $1,265.30