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 $240.74   11.122%   $267.5151   $267.52   $267.50   $267.50  
  Purchase #2 $50.88   5.115%   $53.4825   $53.48   $53.50   $53.50  
  Purchase #3 $201.29   9.405%   $220.2213   $220.22   $220.20   $220.20  
  Purchase #4 $94.70   12.454%   $106.4939   $106.49   $106.50   $106.50  
  Purchase #5 $165.76   6.224%   $176.0769   $176.08   $176.10   $176.10  
  Purchase #6 $23.64   9.402%   $25.8626   $25.86   $25.85   $25.90  
  Purchase #7 $192.75   4.366%   $201.1655   $201.17   $201.15   $201.20  
  7 purchase totals = $969.76       $1,050.8178   $1,050.82   $1,050.80   $1,050.90