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 $204.67   11.460%   $228.1252   $228.13   $228.15   $228.10  
  Purchase #2 $213.50   12.344%   $239.8544   $239.85   $239.85   $239.90  
  Purchase #3 $90.41   7.132%   $96.858   $96.86   $96.85   $96.90  
  Purchase #4 $199.33   8.342%   $215.9581   $215.96   $215.95   $216.00  
  Purchase #5 $93.90   9.671%   $102.9811   $102.98   $103.00   $103.00  
  Purchase #6 $146.44   12.701%   $165.0393   $165.04   $165.05   $165.00  
  Purchase #7 $95.84   12.775%   $108.0836   $108.08   $108.10   $108.10  
  7 purchase totals = $1,044.09       $1,156.8997   $1,156.90   $1,156.95   $1,157.00