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 $180.86   11.164%   $201.0512   $201.05   $201.05   $201.10  
  Purchase #2 $225.54   9.366%   $246.6641   $246.66   $246.65   $246.70  
  Purchase #3 $102.34   6.304%   $108.7915   $108.79   $108.80   $108.80  
  Purchase #4 $221.51   12.774%   $249.8057   $249.81   $249.80   $249.80  
  Purchase #5 $38.53   12.475%   $43.3366   $43.34   $43.35   $43.30  
  Purchase #6 $87.90   5.520%   $92.7521   $92.75   $92.75   $92.80  
  Purchase #7 $147.30   10.871%   $163.313   $163.31   $163.30   $163.30  
  7 purchase totals = $1,003.98       $1,105.7142   $1,105.71   $1,105.70   $1,105.80