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 $210.79   11.732%   $235.5199   $235.52   $235.50   $235.50  
  Purchase #2 $26.32   10.147%   $28.9907   $28.99   $29.00   $29.00  
  Purchase #3 $87.66   11.396%   $97.6497   $97.65   $97.65   $97.60  
  Purchase #4 $94.81   9.326%   $103.652   $103.65   $103.65   $103.70  
  Purchase #5 $216.77   12.190%   $243.1943   $243.19   $243.20   $243.20  
  Purchase #6 $67.47   10.668%   $74.6677   $74.67   $74.65   $74.70  
  Purchase #7 $207.97   11.663%   $232.2255   $232.23   $232.25   $232.20  
  7 purchase totals = $911.79       $1,015.8998   $1,015.90   $1,015.90   $1,015.90