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 $61.52   7.267%   $65.9907   $65.99   $66.00   $66.00  
  Purchase #2 $232.33   9.722%   $254.9171   $254.92   $254.90   $254.90  
  Purchase #3 $85.90   9.663%   $94.2005   $94.20   $94.20   $94.20  
  Purchase #4 $231.87   3.375%   $239.6956   $239.70   $239.70   $239.70  
  Purchase #5 $167.29   12.635%   $188.4271   $188.43   $188.45   $188.40  
  Purchase #6 $48.77   9.320%   $53.3154   $53.32   $53.30   $53.30  
  Purchase #7 $164.90   7.276%   $176.8981   $176.90   $176.90   $176.90  
  7 purchase totals = $992.58       $1,073.4445   $1,073.46   $1,073.45   $1,073.40