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 $238.94   9.843%   $262.4589   $262.46   $262.45   $262.50  
  Purchase #2 $118.60   4.508%   $123.9465   $123.95   $123.95   $123.90  
  Purchase #3 $203.97   13.869%   $232.2586   $232.26   $232.25   $232.30  
  Purchase #4 $138.68   6.641%   $147.8897   $147.89   $147.90   $147.90  
  Purchase #5 $195.29   3.312%   $201.758   $201.76   $201.75   $201.80  
  Purchase #6 $114.52   13.219%   $129.6584   $129.66   $129.65   $129.70  
  Purchase #7 $22.97   12.135%   $25.7574   $25.76   $25.75   $25.80  
  7 purchase totals = $1,032.97       $1,123.7275   $1,123.74   $1,123.70   $1,123.90