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 $244.56   12.689%   $275.5922   $275.59   $275.60   $275.60  
  Purchase #2 $23.82   3.446%   $24.6408   $24.64   $24.65   $24.60  
  Purchase #3 $229.70   7.510%   $246.9505   $246.95   $246.95   $247.00  
  Purchase #4 $97.28   9.773%   $106.7872   $106.79   $106.80   $106.80  
  Purchase #5 $235.77   9.322%   $257.7485   $257.75   $257.75   $257.70  
  Purchase #6 $189.29   8.713%   $205.7828   $205.78   $205.80   $205.80  
  Purchase #7 $53.67   3.587%   $55.5951   $55.60   $55.60   $55.60  
  7 purchase totals = $1,074.09       $1,173.0971   $1,173.10   $1,173.15   $1,173.10