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 $110.72   6.748%   $118.1914   $118.19   $118.20   $118.20  
  Purchase #2 $225.91   11.329%   $251.5033   $251.50   $251.50   $251.50  
  Purchase #3 $53.83   12.702%   $60.6675   $60.67   $60.65   $60.70  
  Purchase #4 $111.71   7.459%   $120.0424   $120.04   $120.05   $120.00  
  Purchase #5 $122.79   11.131%   $136.4578   $136.46   $136.45   $136.50  
  Purchase #6 $155.71   3.355%   $160.9341   $160.93   $160.95   $160.90  
  Purchase #7 $179.54   12.501%   $201.9843   $201.98   $202.00   $202.00  
  7 purchase totals = $960.21       $1,049.7808   $1,049.77   $1,049.80   $1,049.80