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 $86.44   9.649%   $94.7806   $94.78   $94.80   $94.80  
  Purchase #2 $68.49   5.207%   $72.0563   $72.06   $72.05   $72.10  
  Purchase #3 $153.55   9.178%   $167.6428   $167.64   $167.65   $167.60  
  Purchase #4 $194.52   8.726%   $211.4938   $211.49   $211.50   $211.50  
  Purchase #5 $28.97   8.618%   $31.4666   $31.47   $31.45   $31.50  
  Purchase #6 $193.34   4.333%   $201.7174   $201.72   $201.70   $201.70  
  Purchase #7 $67.98   7.311%   $72.95   $72.95   $72.95   $73.00  
  7 purchase totals = $793.29       $852.1075   $852.11   $852.10   $852.20