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 $62.40   13.251%   $70.6686   $70.67   $70.65   $70.70  
  Purchase #2 $113.65   6.226%   $120.7258   $120.73   $120.75   $120.70  
  Purchase #3 $235.84   11.265%   $262.4074   $262.41   $262.40   $262.40  
  Purchase #4 $65.82   9.310%   $71.9478   $71.95   $71.95   $71.90  
  Purchase #5 $60.67   4.563%   $63.4384   $63.44   $63.45   $63.40  
  Purchase #6 $198.34   4.770%   $207.8008   $207.80   $207.80   $207.80  
  Purchase #7 $204.34   10.631%   $226.0634   $226.06   $226.05   $226.10  
  7 purchase totals = $941.06       $1,023.0522   $1,023.06   $1,023.05   $1,023.00