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 $156.76   9.569%   $171.7604   $171.76   $171.75   $171.80  
  Purchase #2 $173.47   6.183%   $184.1957   $184.20   $184.20   $184.20  
  Purchase #3 $91.45   12.305%   $102.7029   $102.70   $102.70   $102.70  
  Purchase #4 $90.47   7.293%   $97.068   $97.07   $97.05   $97.10  
  Purchase #5 $195.82   6.717%   $208.9732   $208.97   $208.95   $209.00  
  Purchase #6 $156.62   9.185%   $171.0055   $171.01   $171.00   $171.00  
  Purchase #7 $23.97   4.352%   $25.0132   $25.01   $25.00   $25.00  
  7 purchase totals = $888.56       $960.7189   $960.72   $960.65   $960.80