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 $239.89   5.363%   $252.7553   $252.76   $252.75   $252.80  
  Purchase #2 $153.94   4.293%   $160.5486   $160.55   $160.55   $160.50  
  Purchase #3 $32.96   11.648%   $36.7992   $36.80   $36.80   $36.80  
  Purchase #4 $200.81   5.814%   $212.4851   $212.49   $212.50   $212.50  
  Purchase #5 $188.90   5.871%   $199.9903   $199.99   $200.00   $200.00  
  Purchase #6 $180.59   12.270%   $202.7484   $202.75   $202.75   $202.70  
  Purchase #7 $29.26   12.565%   $32.9365   $32.94   $32.95   $32.90  
  7 purchase totals = $1,026.35       $1,098.2634   $1,098.28   $1,098.30   $1,098.20