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 $244.79   9.306%   $267.5702   $267.57   $267.55   $267.60  
  Purchase #2 $66.84   4.412%   $69.789   $69.79   $69.80   $69.80  
  Purchase #3 $148.39   13.206%   $167.9864   $167.99   $168.00   $168.00  
  Purchase #4 $131.70   7.444%   $141.5037   $141.50   $141.50   $141.50  
  Purchase #5 $147.72   8.347%   $160.0502   $160.05   $160.05   $160.10  
  Purchase #6 $45.84   8.705%   $49.8304   $49.83   $49.85   $49.80  
  Purchase #7 $179.58   12.453%   $201.9431   $201.94   $201.95   $201.90  
  7 purchase totals = $964.86       $1,058.6730   $1,058.67   $1,058.70   $1,058.70