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 $201.77   12.555%   $227.1022   $227.10   $227.10   $227.10  
  Purchase #2 $63.36   9.694%   $69.5021   $69.50   $69.50   $69.50  
  Purchase #3 $38.94   13.642%   $44.2522   $44.25   $44.25   $44.30  
  Purchase #4 $126.79   9.585%   $138.9428   $138.94   $138.95   $138.90  
  Purchase #5 $191.75   12.874%   $216.4359   $216.44   $216.45   $216.40  
  Purchase #6 $201.79   12.475%   $226.9633   $226.96   $226.95   $227.00  
  Purchase #7 $169.51   7.245%   $181.791   $181.79   $181.80   $181.80  
  7 purchase totals = $993.91       $1,104.9895   $1,104.98   $1,105.00   $1,105.00