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 $157.64   11.764%   $176.1848   $176.18   $176.20   $176.20  
  Purchase #2 $235.99   7.595%   $253.9134   $253.91   $253.90   $253.90  
  Purchase #3 $170.87   9.560%   $187.2052   $187.21   $187.20   $187.20  
  Purchase #4 $76.91   11.203%   $85.5262   $85.53   $85.55   $85.50  
  Purchase #5 $202.31   4.803%   $212.0269   $212.03   $212.05   $212.00  
  Purchase #6 $138.49   6.770%   $147.8658   $147.87   $147.85   $147.90  
  Purchase #7 $82.33   10.608%   $91.0636   $91.06   $91.05   $91.10  
  7 purchase totals = $1,064.54       $1,153.7859   $1,153.79   $1,153.80   $1,153.80