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 $53.87   9.500%   $58.9877   $58.99   $59.00   $59.00  
  Purchase #2 $116.79   8.361%   $126.5548   $126.55   $126.55   $126.60  
  Purchase #3 $88.97   5.746%   $94.0822   $94.08   $94.10   $94.10  
  Purchase #4 $250.40   7.509%   $269.2025   $269.20   $269.20   $269.20  
  Purchase #5 $138.69   5.157%   $145.8422   $145.84   $145.85   $145.80  
  Purchase #6 $233.69   5.719%   $247.0547   $247.05   $247.05   $247.10  
  Purchase #7 $115.94   8.753%   $126.0882   $126.09   $126.10   $126.10  
  7 purchase totals = $998.35       $1,067.8123   $1,067.80   $1,067.85   $1,067.90