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 $53.68   7.591%   $57.7548   $57.75   $57.75   $57.80  
  Purchase #2 $224.93   9.219%   $245.6663   $245.67   $245.65   $245.70  
  Purchase #3 $195.68   5.791%   $207.0118   $207.01   $207.00   $207.00  
  Purchase #4 $201.46   10.808%   $223.2338   $223.23   $223.25   $223.20  
  Purchase #5 $190.29   13.373%   $215.7375   $215.74   $215.75   $215.70  
  Purchase #6 $96.52   10.367%   $106.5262   $106.53   $106.55   $106.50  
  Purchase #7 $184.52   8.847%   $200.8445   $200.84   $200.85   $200.80  
  7 purchase totals = $1,147.08       $1,256.7749   $1,256.77   $1,256.80   $1,256.70