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 $217.38   7.122%   $232.8618   $232.86   $232.85   $232.90  
  Purchase #2 $139.69   9.529%   $153.0011   $153.00   $153.00   $153.00  
  Purchase #3 $56.93   7.490%   $61.1941   $61.19   $61.20   $61.20  
  Purchase #4 $111.83   5.321%   $117.7805   $117.78   $117.80   $117.80  
  Purchase #5 $67.95   4.678%   $71.1287   $71.13   $71.15   $71.10  
  Purchase #6 $187.66   7.169%   $201.1133   $201.11   $201.10   $201.10  
  Purchase #7 $41.52   6.172%   $44.0826   $44.08   $44.10   $44.10  
  7 purchase totals = $822.96       $881.1621   $881.15   $881.20   $881.20